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 $245.81   6.661%   $262.1834   $262.18   $262.20   $262.20  
  Purchase #2 $228.75   6.858%   $244.4377   $244.44   $244.45   $244.40  
  Purchase #3 $83.67   9.196%   $91.3643   $91.36   $91.35   $91.40  
  Purchase #4 $126.61   11.516%   $141.1904   $141.19   $141.20   $141.20  
  Purchase #5 $194.72   7.564%   $209.4486   $209.45   $209.45   $209.40  
  Purchase #6 $57.99   9.360%   $63.4179   $63.42   $63.40   $63.40  
  Purchase #7 $230.78   10.504%   $255.0211   $255.02   $255.00   $255.00  
  7 purchase totals = $1,168.33       $1,267.0634   $1,267.06   $1,267.05   $1,267.00