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 $181.48   8.854%   $197.5482   $197.55   $197.55   $197.50  
  Purchase #2 $174.55   4.451%   $182.3192   $182.32   $182.30   $182.30  
  Purchase #3 $8.93   5.124%   $9.3876   $9.39   $9.40   $9.40  
  Purchase #4 $84.44   3.459%   $87.3608   $87.36   $87.35   $87.40  
  Purchase #5 $130.78   5.196%   $137.5753   $137.58   $137.60   $137.60  
  Purchase #6 $141.85   5.690%   $149.9213   $149.92   $149.90   $149.90  
  Purchase #7 $228.51   3.492%   $236.4896   $236.49   $236.50   $236.50  
  7 purchase totals = $950.54       $1,000.6020   $1,000.61   $1,000.60   $1,000.60