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 $69.90   8.780%   $76.0372   $76.04   $76.05   $76.00  
  Purchase #2 $238.81   11.741%   $266.8487   $266.85   $266.85   $266.80  
  Purchase #3 $20.25   13.667%   $23.0176   $23.02   $23.00   $23.00  
  Purchase #4 $178.46   4.814%   $187.0511   $187.05   $187.05   $187.10  
  Purchase #5 $28.59   9.336%   $31.2592   $31.26   $31.25   $31.30  
  Purchase #6 $143.69   4.628%   $150.34   $150.34   $150.35   $150.30  
  Purchase #7 $104.85   12.494%   $117.95   $117.95   $117.95   $118.00  
  7 purchase totals = $784.55       $852.5038   $852.51   $852.50   $852.50