Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $147.77   13.501%   $167.7204   $167.72   $167.70   $167.70  
  Purchase #2 $248.51   3.658%   $257.6005   $257.60   $257.60   $257.60  
  Purchase #3 $211.46   11.480%   $235.7356   $235.74   $235.75   $235.70  
  Purchase #4 $108.93   6.377%   $115.8765   $115.88   $115.90   $115.90  
  Purchase #5 $122.88   10.524%   $135.8119   $135.81   $135.80   $135.80  
  Purchase #6 $184.94   10.178%   $203.7632   $203.76   $203.75   $203.80  
  Purchase #7 $171.39   8.226%   $185.4885   $185.49   $185.50   $185.50  
  7 purchase totals = $1,195.88       $1,301.9966   $1,302.00   $1,302.00   $1,302.00