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 $142.97   7.692%   $153.9673   $153.97   $153.95   $154.00  
  Purchase #2 $158.28   12.470%   $178.0175   $178.02   $178.00   $178.00  
  Purchase #3 $13.90   4.290%   $14.4963   $14.50   $14.50   $14.50  
  Purchase #4 $153.95   4.204%   $160.4221   $160.42   $160.40   $160.40  
  Purchase #5 $96.49   3.387%   $99.7581   $99.76   $99.75   $99.80  
  Purchase #6 $215.62   9.666%   $236.4618   $236.46   $236.45   $236.50  
  Purchase #7 $194.85   3.694%   $202.0478   $202.05   $202.05   $202.00  
  7 purchase totals = $976.06       $1,045.1709   $1,045.18   $1,045.10   $1,045.20