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 $228.50   5.552%   $241.1863   $241.19   $241.20   $241.20  
  Purchase #2 $138.41   12.565%   $155.8012   $155.80   $155.80   $155.80  
  Purchase #3 $38.67   4.583%   $40.4422   $40.44   $40.45   $40.40  
  Purchase #4 $229.25   4.819%   $240.2976   $240.30   $240.30   $240.30  
  Purchase #5 $13.73   5.614%   $14.5008   $14.50   $14.50   $14.50  
  Purchase #6 $52.41   11.538%   $58.4571   $58.46   $58.45   $58.50  
  Purchase #7 $191.96   5.586%   $202.6829   $202.68   $202.70   $202.70  
  7 purchase totals = $892.93       $953.3681   $953.37   $953.40   $953.40