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 $35.31   8.546%   $38.3276   $38.33   $38.35   $38.30  
  Purchase #2 $228.77   5.393%   $241.1076   $241.11   $241.10   $241.10  
  Purchase #3 $236.26   3.121%   $243.6337   $243.63   $243.65   $243.60  
  Purchase #4 $47.91   11.562%   $53.4494   $53.45   $53.45   $53.40  
  Purchase #5 $150.26   5.830%   $159.0202   $159.02   $159.00   $159.00  
  Purchase #6 $96.34   13.390%   $109.2399   $109.24   $109.25   $109.20  
  Purchase #7 $91.40   6.422%   $97.2697   $97.27   $97.25   $97.30  
  7 purchase totals = $886.25       $942.0481   $942.05   $942.05   $941.90