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 $246.80   6.386%   $262.5606   $262.56   $262.55   $262.60  
  Purchase #2 $184.51   7.554%   $198.4479   $198.45   $198.45   $198.40  
  Purchase #3 $135.49   8.366%   $146.8251   $146.83   $146.85   $146.80  
  Purchase #4 $181.58   12.676%   $204.5971   $204.60   $204.60   $204.60  
  Purchase #5 $57.69   7.676%   $62.1183   $62.12   $62.10   $62.10  
  Purchase #6 $231.85   7.135%   $248.3925   $248.39   $248.40   $248.40  
  Purchase #7 $212.42   11.566%   $236.9885   $236.99   $237.00   $237.00  
  7 purchase totals = $1,250.34       $1,359.9300   $1,359.94   $1,359.95   $1,359.90