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 $117.84   3.571%   $122.0481   $122.05   $122.05   $122.00  
  Purchase #2 $75.64   3.343%   $78.1686   $78.17   $78.15   $78.20  
  Purchase #3 $84.76   7.847%   $91.4111   $91.41   $91.40   $91.40  
  Purchase #4 $119.58   9.387%   $130.805   $130.81   $130.80   $130.80  
  Purchase #5 $199.45   13.391%   $226.1583   $226.16   $226.15   $226.20  
  Purchase #6 $131.54   11.407%   $146.5448   $146.54   $146.55   $146.50  
  Purchase #7 $230.96   10.742%   $255.7697   $255.77   $255.75   $255.80  
  7 purchase totals = $959.77       $1,050.9056   $1,050.91   $1,050.85   $1,050.90