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 $211.69   11.271%   $235.5496   $235.55   $235.55   $235.50  
  Purchase #2 $45.98   7.436%   $49.3991   $49.40   $49.40   $49.40  
  Purchase #3 $198.53   4.274%   $207.0152   $207.02   $207.00   $207.00  
  Purchase #4 $207.91   5.123%   $218.5612   $218.56   $218.55   $218.60  
  Purchase #5 $116.50   8.583%   $126.4992   $126.50   $126.50   $126.50  
  Purchase #6 $57.43   5.178%   $60.4037   $60.40   $60.40   $60.40  
  Purchase #7 $206.99   5.827%   $219.0513   $219.05   $219.05   $219.10  
  7 purchase totals = $1,045.03       $1,116.4793   $1,116.48   $1,116.45   $1,116.50