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 $59.41   11.135%   $66.0253   $66.03   $66.05   $66.00  
  Purchase #2 $112.34   7.332%   $120.5768   $120.58   $120.60   $120.60  
  Purchase #3 $44.99   3.867%   $46.7298   $46.73   $46.75   $46.70  
  Purchase #4 $123.66   5.171%   $130.0545   $130.05   $130.05   $130.10  
  Purchase #5 $236.94   4.616%   $247.8772   $247.88   $247.90   $247.90  
  Purchase #6 $124.98   3.310%   $129.1168   $129.12   $129.10   $129.10  
  Purchase #7 $122.67   4.302%   $127.9473   $127.95   $127.95   $127.90  
  7 purchase totals = $824.99       $868.3277   $868.34   $868.40   $868.30