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 $137.58   6.310%   $146.2613   $146.26   $146.25   $146.30  
  Purchase #2 $198.27   6.742%   $211.6374   $211.64   $211.65   $211.60  
  Purchase #3 $167.67   8.733%   $182.3126   $182.31   $182.30   $182.30  
  Purchase #4 $158.95   7.149%   $170.3133   $170.31   $170.30   $170.30  
  Purchase #5 $31.32   3.769%   $32.5005   $32.50   $32.50   $32.50  
  Purchase #6 $33.31   4.346%   $34.7577   $34.76   $34.75   $34.80  
  Purchase #7 $223.43   8.536%   $242.502   $242.50   $242.50   $242.50  
  7 purchase totals = $950.53       $1,020.2848   $1,020.28   $1,020.25   $1,020.30