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 $67.99   10.108%   $74.8624   $74.86   $74.85   $74.90  
  Purchase #2 $165.58   4.406%   $172.8755   $172.88   $172.90   $172.90  
  Purchase #3 $154.80   12.265%   $173.7862   $173.79   $173.80   $173.80  
  Purchase #4 $95.75   9.147%   $104.5083   $104.51   $104.50   $104.50  
  Purchase #5 $126.64   7.369%   $135.9721   $135.97   $135.95   $136.00  
  Purchase #6 $58.58   8.636%   $63.639   $63.64   $63.65   $63.60  
  Purchase #7 $33.43   6.863%   $35.7243   $35.72   $35.70   $35.70  
  7 purchase totals = $702.77       $761.3678   $761.37   $761.35   $761.40