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 $60.72   4.506%   $63.456   $63.46   $63.45   $63.50  
  Purchase #2 $12.59   7.245%   $13.5021   $13.50   $13.50   $13.50  
  Purchase #3 $139.64   7.350%   $149.9035   $149.90   $149.90   $149.90  
  Purchase #4 $150.70   11.732%   $168.3801   $168.38   $168.40   $168.40  
  Purchase #5 $117.35   11.460%   $130.7983   $130.80   $130.80   $130.80  
  Purchase #6 $41.69   12.286%   $46.812   $46.81   $46.80   $46.80  
  Purchase #7 $184.48   13.675%   $209.7076   $209.71   $209.70   $209.70  
  7 purchase totals = $707.17       $782.5596   $782.56   $782.55   $782.60