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 $200.58   12.655%   $225.9634   $225.96   $225.95   $226.00  
  Purchase #2 $134.75   3.371%   $139.2924   $139.29   $139.30   $139.30  
  Purchase #3 $116.53   12.182%   $130.7257   $130.73   $130.75   $130.70  
  Purchase #4 $149.55   13.787%   $170.1685   $170.17   $170.15   $170.20  
  Purchase #5 $64.65   6.661%   $68.9563   $68.96   $68.95   $69.00  
  Purchase #6 $147.27   11.862%   $164.7392   $164.74   $164.75   $164.70  
  Purchase #7 $114.54   3.578%   $118.6382   $118.64   $118.65   $118.60  
  7 purchase totals = $927.87       $1,018.4837   $1,018.49   $1,018.50   $1,018.50