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 $202.28   4.729%   $211.8458   $211.85   $211.85   $211.80  
  Purchase #2 $131.65   3.200%   $135.8628   $135.86   $135.85   $135.90  
  Purchase #3 $215.53   5.272%   $226.8927   $226.89   $226.90   $226.90  
  Purchase #4 $43.76   4.812%   $45.8657   $45.87   $45.85   $45.90  
  Purchase #5 $67.83   13.483%   $76.9755   $76.98   $77.00   $77.00  
  Purchase #6 $129.46   9.645%   $141.9464   $141.95   $141.95   $141.90  
  Purchase #7 $166.40   10.524%   $183.9119   $183.91   $183.90   $183.90  
  7 purchase totals = $956.91       $1,023.3008   $1,023.31   $1,023.30   $1,023.30