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 $224.96   12.806%   $253.7684   $253.77   $253.75   $253.80  
  Purchase #2 $241.42   4.307%   $251.818   $251.82   $251.80   $251.80  
  Purchase #3 $238.79   11.545%   $266.3583   $266.36   $266.35   $266.40  
  Purchase #4 $98.71   5.142%   $103.7857   $103.79   $103.80   $103.80  
  Purchase #5 $110.25   10.540%   $121.8704   $121.87   $121.85   $121.90  
  Purchase #6 $24.28   6.621%   $25.8876   $25.89   $25.90   $25.90  
  Purchase #7 $63.64   11.213%   $70.776   $70.78   $70.80   $70.80  
  7 purchase totals = $1,002.05       $1,094.2644   $1,094.28   $1,094.25   $1,094.40