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 $246.93   5.184%   $259.7309   $259.73   $259.75   $259.70  
  Purchase #2 $92.44   4.299%   $96.414   $96.41   $96.40   $96.40  
  Purchase #3 $14.40   5.144%   $15.1407   $15.14   $15.15   $15.10  
  Purchase #4 $204.41   10.564%   $226.0039   $226.00   $226.00   $226.00  
  Purchase #5 $187.49   13.850%   $213.4574   $213.46   $213.45   $213.50  
  Purchase #6 $49.63   4.797%   $52.0108   $52.01   $52.00   $52.00  
  Purchase #7 $213.40   11.824%   $238.6324   $238.63   $238.65   $238.60  
  7 purchase totals = $1,008.70       $1,101.3901   $1,101.38   $1,101.40   $1,101.30