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 $39.46   3.792%   $40.9563   $40.96   $40.95   $41.00  
  Purchase #2 $238.62   7.232%   $255.877   $255.88   $255.90   $255.90  
  Purchase #3 $119.36   5.179%   $125.5417   $125.54   $125.55   $125.50  
  Purchase #4 $223.55   9.810%   $245.4803   $245.48   $245.50   $245.50  
  Purchase #5 $249.92   12.314%   $280.6951   $280.70   $280.70   $280.70  
  Purchase #6 $203.56   9.795%   $223.4987   $223.50   $223.50   $223.50  
  Purchase #7 $33.52   7.587%   $36.0632   $36.06   $36.05   $36.10  
  7 purchase totals = $1,107.99       $1,208.1123   $1,208.12   $1,208.15   $1,208.20