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 $107.70   10.533%   $119.044   $119.04   $119.05   $119.00  
  Purchase #2 $232.67   10.779%   $257.7495   $257.75   $257.75   $257.70  
  Purchase #3 $146.59   6.209%   $155.6918   $155.69   $155.70   $155.70  
  Purchase #4 $166.43   5.708%   $175.9298   $175.93   $175.95   $175.90  
  Purchase #5 $176.98   11.832%   $197.9203   $197.92   $197.90   $197.90  
  Purchase #6 $54.26   9.385%   $59.3523   $59.35   $59.35   $59.40  
  Purchase #7 $167.26   11.571%   $186.6137   $186.61   $186.60   $186.60  
  7 purchase totals = $1,051.89       $1,152.3014   $1,152.29   $1,152.30   $1,152.20