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 $234.86   6.103%   $249.1935   $249.19   $249.20   $249.20  
  Purchase #2 $196.48   3.160%   $202.6888   $202.69   $202.70   $202.70  
  Purchase #3 $66.51   4.798%   $69.7011   $69.70   $69.70   $69.70  
  Purchase #4 $48.80   4.416%   $50.955   $50.96   $50.95   $51.00  
  Purchase #5 $44.53   9.320%   $48.6802   $48.68   $48.70   $48.70  
  Purchase #6 $117.43   3.846%   $121.9464   $121.95   $121.95   $121.90  
  Purchase #7 $75.62   11.587%   $84.3821   $84.38   $84.40   $84.40  
  7 purchase totals = $784.23       $827.5471   $827.55   $827.60   $827.60