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 $83.36   11.294%   $92.7747   $92.77   $92.75   $92.80  
  Purchase #2 $216.25   9.261%   $236.2769   $236.28   $236.30   $236.30  
  Purchase #3 $147.39   11.237%   $163.9522   $163.95   $163.95   $164.00  
  Purchase #4 $49.72   9.250%   $54.3191   $54.32   $54.30   $54.30  
  Purchase #5 $5.55   10.190%   $6.1155   $6.12   $6.10   $6.10  
  Purchase #6 $236.97   6.363%   $252.0484   $252.05   $252.05   $252.00  
  Purchase #7 $178.49   6.299%   $189.7331   $189.73   $189.75   $189.70  
  7 purchase totals = $917.73       $995.2199   $995.22   $995.20   $995.20