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 $235.84   5.422%   $248.6272   $248.63   $248.65   $248.60  
  Purchase #2 $229.68   7.753%   $247.4871   $247.49   $247.50   $247.50  
  Purchase #3 $203.35   6.717%   $217.009   $217.01   $217.00   $217.00  
  Purchase #4 $119.69   3.531%   $123.9163   $123.92   $123.90   $123.90  
  Purchase #5 $140.68   8.205%   $152.2228   $152.22   $152.20   $152.20  
  Purchase #6 $135.66   11.264%   $150.9407   $150.94   $150.95   $150.90  
  Purchase #7 $112.38   5.598%   $118.671   $118.67   $118.65   $118.70  
  7 purchase totals = $1,177.28       $1,258.8741   $1,258.88   $1,258.85   $1,258.80