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 $87.94   6.215%   $93.4055   $93.41   $93.40   $93.40  
  Purchase #2 $116.89   8.295%   $126.586   $126.59   $126.60   $126.60  
  Purchase #3 $225.34   8.301%   $244.0455   $244.05   $244.05   $244.00  
  Purchase #4 $219.97   13.772%   $250.2643   $250.26   $250.25   $250.30  
  Purchase #5 $82.89   10.520%   $91.61   $91.61   $91.60   $91.60  
  Purchase #6 $126.51   6.453%   $134.6737   $134.67   $134.65   $134.70  
  Purchase #7 $194.78   5.634%   $205.7539   $205.75   $205.75   $205.80  
  7 purchase totals = $1,054.32       $1,146.3389   $1,146.34   $1,146.30   $1,146.40