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 $55.39   9.288%   $60.5346   $60.53   $60.55   $60.50  
  Purchase #2 $213.37   5.712%   $225.5577   $225.56   $225.55   $225.60  
  Purchase #3 $60.76   5.133%   $63.8788   $63.88   $63.90   $63.90  
  Purchase #4 $10.61   13.247%   $12.0155   $12.02   $12.00   $12.00  
  Purchase #5 $22.73   6.782%   $24.2715   $24.27   $24.25   $24.30  
  Purchase #6 $249.29   11.287%   $277.4274   $277.43   $277.45   $277.40  
  Purchase #7 $213.77   3.663%   $221.6004   $221.60   $221.60   $221.60  
  7 purchase totals = $825.92       $885.2859   $885.29   $885.30   $885.30