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 $194.65   4.212%   $202.8487   $202.85   $202.85   $202.80  
  Purchase #2 $138.97   8.633%   $150.9673   $150.97   $150.95   $151.00  
  Purchase #3 $165.31   3.174%   $170.5569   $170.56   $170.55   $170.60  
  Purchase #4 $125.72   10.829%   $139.3342   $139.33   $139.35   $139.30  
  Purchase #5 $81.37   9.492%   $89.0936   $89.09   $89.10   $89.10  
  Purchase #6 $235.96   8.312%   $255.573   $255.57   $255.55   $255.60  
  Purchase #7 $225.66   9.283%   $246.608   $246.61   $246.60   $246.60  
  7 purchase totals = $1,167.64       $1,254.9817   $1,254.98   $1,254.95   $1,255.00