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 $53.77   11.476%   $59.9406   $59.94   $59.95   $59.90  
  Purchase #2 $243.63   11.731%   $272.2102   $272.21   $272.20   $272.20  
  Purchase #3 $186.36   4.751%   $195.214   $195.21   $195.20   $195.20  
  Purchase #4 $122.92   10.586%   $135.9323   $135.93   $135.95   $135.90  
  Purchase #5 $68.93   13.441%   $78.1949   $78.19   $78.20   $78.20  
  Purchase #6 $117.78   13.600%   $133.7981   $133.80   $133.80   $133.80  
  Purchase #7 $229.47   6.848%   $245.1841   $245.18   $245.20   $245.20  
  7 purchase totals = $1,022.86       $1,120.4742   $1,120.46   $1,120.50   $1,120.40