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 $62.42   3.598%   $64.6659   $64.67   $64.65   $64.70  
  Purchase #2 $32.34   4.186%   $33.6938   $33.69   $33.70   $33.70  
  Purchase #3 $59.81   11.276%   $66.5542   $66.55   $66.55   $66.60  
  Purchase #4 $99.83   13.479%   $113.2861   $113.29   $113.30   $113.30  
  Purchase #5 $23.78   8.829%   $25.8795   $25.88   $25.90   $25.90  
  Purchase #6 $198.45   5.210%   $208.7892   $208.79   $208.80   $208.80  
  Purchase #7 $235.49   3.621%   $244.0171   $244.02   $244.00   $244.00  
  7 purchase totals = $712.12       $756.8858   $756.89   $756.90   $757.00