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 $238.62   4.174%   $248.58   $248.58   $248.60   $248.60  
  Purchase #2 $217.86   8.303%   $235.9489   $235.95   $235.95   $235.90  
  Purchase #3 $58.92   3.769%   $61.1407   $61.14   $61.15   $61.10  
  Purchase #4 $59.84   4.302%   $62.4143   $62.41   $62.40   $62.40  
  Purchase #5 $116.42   13.727%   $132.401   $132.40   $132.40   $132.40  
  Purchase #6 $7.26   4.620%   $7.5954   $7.60   $7.60   $7.60  
  Purchase #7 $161.79   11.124%   $179.7875   $179.79   $179.80   $179.80  
  7 purchase totals = $860.71       $927.8678   $927.87   $927.90   $927.80