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 $54.47   9.571%   $59.6833   $59.68   $59.70   $59.70  
  Purchase #2 $204.72   10.320%   $225.8471   $225.85   $225.85   $225.80  
  Purchase #3 $215.94   6.381%   $229.7191   $229.72   $229.70   $229.70  
  Purchase #4 $211.47   8.185%   $228.7788   $228.78   $228.80   $228.80  
  Purchase #5 $109.95   6.143%   $116.7042   $116.70   $116.70   $116.70  
  Purchase #6 $135.82   7.779%   $146.3854   $146.39   $146.40   $146.40  
  Purchase #7 $223.79   10.165%   $246.5383   $246.54   $246.55   $246.50  
  7 purchase totals = $1,156.16       $1,253.6562   $1,253.66   $1,253.70   $1,253.60