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 $250.56   6.364%   $266.5056   $266.51   $266.50   $266.50  
  Purchase #2 $250.33   12.753%   $282.2546   $282.25   $282.25   $282.30  
  Purchase #3 $155.36   13.343%   $176.0897   $176.09   $176.10   $176.10  
  Purchase #4 $91.74   3.300%   $94.7674   $94.77   $94.75   $94.80  
  Purchase #5 $84.79   9.475%   $92.8239   $92.82   $92.80   $92.80  
  Purchase #6 $67.49   10.353%   $74.4772   $74.48   $74.50   $74.50  
  Purchase #7 $54.74   7.244%   $58.7054   $58.71   $58.70   $58.70  
  7 purchase totals = $955.01       $1,045.6238   $1,045.63   $1,045.60   $1,045.70