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 $125.56   12.646%   $141.4383   $141.44   $141.45   $141.40  
  Purchase #2 $118.97   11.264%   $132.3708   $132.37   $132.35   $132.40  
  Purchase #3 $170.25   6.546%   $181.3946   $181.39   $181.40   $181.40  
  Purchase #4 $236.52   4.241%   $246.5508   $246.55   $246.55   $246.60  
  Purchase #5 $135.69   12.638%   $152.8385   $152.84   $152.85   $152.80  
  Purchase #6 $19.60   4.235%   $20.4301   $20.43   $20.45   $20.40  
  Purchase #7 $138.77   6.685%   $148.0468   $148.05   $148.05   $148.00  
  7 purchase totals = $945.36       $1,023.0699   $1,023.07   $1,023.10   $1,023.00