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 $61.51   11.428%   $68.5394   $68.54   $68.55   $68.50  
  Purchase #2 $121.50   13.177%   $137.5101   $137.51   $137.50   $137.50  
  Purchase #3 $249.41   3.814%   $258.9225   $258.92   $258.90   $258.90  
  Purchase #4 $194.80   12.834%   $219.8006   $219.80   $219.80   $219.80  
  Purchase #5 $24.92   8.656%   $27.0771   $27.08   $27.10   $27.10  
  Purchase #6 $124.88   5.223%   $131.4025   $131.40   $131.40   $131.40  
  Purchase #7 $162.89   9.818%   $178.8825   $178.88   $178.90   $178.90  
  7 purchase totals = $939.91       $1,022.1347   $1,022.13   $1,022.15   $1,022.10