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 $218.32   10.721%   $241.7261   $241.73   $241.75   $241.70  
  Purchase #2 $193.91   3.370%   $200.4448   $200.44   $200.45   $200.40  
  Purchase #3 $225.72   7.643%   $242.9718   $242.97   $242.95   $243.00  
  Purchase #4 $35.29   11.350%   $39.2954   $39.30   $39.30   $39.30  
  Purchase #5 $112.84   5.773%   $119.3543   $119.35   $119.35   $119.40  
  Purchase #6 $54.48   3.300%   $56.2778   $56.28   $56.30   $56.30  
  Purchase #7 $124.28   7.605%   $133.7315   $133.73   $133.75   $133.70  
  7 purchase totals = $964.84       $1,033.8017   $1,033.80   $1,033.85   $1,033.80