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 $53.71   11.421%   $59.8442   $59.84   $59.85   $59.80  
  Purchase #2 $204.44   11.799%   $228.5619   $228.56   $228.55   $228.60  
  Purchase #3 $15.41   6.726%   $16.4465   $16.45   $16.45   $16.40  
  Purchase #4 $59.36   11.121%   $65.9614   $65.96   $65.95   $66.00  
  Purchase #5 $225.33   10.539%   $249.0775   $249.08   $249.10   $249.10  
  Purchase #6 $99.57   8.663%   $108.1957   $108.20   $108.20   $108.20  
  Purchase #7 $32.51   12.243%   $36.4902   $36.49   $36.50   $36.50  
  7 purchase totals = $690.33       $764.5774   $764.58   $764.60   $764.60