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 $57.82   11.468%   $64.4508   $64.45   $64.45   $64.50  
  Purchase #2 $32.37   11.214%   $36   $36.00   $36.00   $36.00  
  Purchase #3 $106.84   3.552%   $110.635   $110.64   $110.65   $110.60  
  Purchase #4 $230.51   11.288%   $256.53   $256.53   $256.55   $256.50  
  Purchase #5 $30.70   10.788%   $34.0119   $34.01   $34.00   $34.00  
  Purchase #6 $185.34   13.494%   $210.3498   $210.35   $210.35   $210.30  
  Purchase #7 $141.27   4.199%   $147.2019   $147.20   $147.20   $147.20  
  7 purchase totals = $784.85       $859.1794   $859.18   $859.20   $859.10