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 $87.28   13.245%   $98.8402   $98.84   $98.85   $98.80  
  Purchase #2 $220.56   9.579%   $241.6874   $241.69   $241.70   $241.70  
  Purchase #3 $66.64   11.364%   $74.213   $74.21   $74.20   $74.20  
  Purchase #4 $126.95   4.752%   $132.9827   $132.98   $133.00   $133.00  
  Purchase #5 $102.75   3.305%   $106.1459   $106.15   $106.15   $106.10  
  Purchase #6 $150.54   9.837%   $165.3486   $165.35   $165.35   $165.30  
  Purchase #7 $50.84   13.126%   $57.5133   $57.51   $57.50   $57.50  
  7 purchase totals = $805.56       $876.7311   $876.73   $876.75   $876.60