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 $248.77   5.168%   $261.6264   $261.63   $261.65   $261.60  
  Purchase #2 $14.45   8.754%   $15.715   $15.72   $15.70   $15.70  
  Purchase #3 $124.46   6.604%   $132.6793   $132.68   $132.70   $132.70  
  Purchase #4 $101.59   8.230%   $109.9509   $109.95   $109.95   $110.00  
  Purchase #5 $202.89   11.243%   $225.7009   $225.70   $225.70   $225.70  
  Purchase #6 $148.51   12.662%   $167.3143   $167.31   $167.30   $167.30  
  Purchase #7 $113.81   7.132%   $121.9269   $121.93   $121.95   $121.90  
  7 purchase totals = $954.48       $1,034.9137   $1,034.92   $1,034.95   $1,034.90