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 $115.68   8.813%   $125.8749   $125.87   $125.85   $125.90  
  Purchase #2 $119.48   13.187%   $135.2358   $135.24   $135.25   $135.20  
  Purchase #3 $26.66   7.112%   $28.5561   $28.56   $28.55   $28.60  
  Purchase #4 $222.51   3.585%   $230.487   $230.49   $230.50   $230.50  
  Purchase #5 $31.40   11.638%   $35.0543   $35.05   $35.05   $35.10  
  Purchase #6 $33.95   3.841%   $35.254   $35.25   $35.25   $35.30  
  Purchase #7 $134.75   12.359%   $151.4038   $151.40   $151.40   $151.40  
  7 purchase totals = $684.43       $741.8659   $741.86   $741.85   $742.00