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 $187.71   7.561%   $201.9028   $201.90   $201.90   $201.90  
  Purchase #2 $135.73   6.734%   $144.8701   $144.87   $144.85   $144.90  
  Purchase #3 $160.67   4.218%   $167.4471   $167.45   $167.45   $167.40  
  Purchase #4 $173.27   5.761%   $183.2521   $183.25   $183.25   $183.30  
  Purchase #5 $175.36   10.425%   $193.6413   $193.64   $193.65   $193.60  
  Purchase #6 $248.80   6.856%   $265.8577   $265.86   $265.85   $265.90  
  Purchase #7 $213.31   4.413%   $222.7234   $222.72   $222.70   $222.70  
  7 purchase totals = $1,294.85       $1,379.6945   $1,379.69   $1,379.65   $1,379.70