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 $212.79   11.333%   $236.9055   $236.91   $236.90   $236.90  
  Purchase #2 $147.69   13.649%   $167.8482   $167.85   $167.85   $167.80  
  Purchase #3 $57.75   12.637%   $65.0479   $65.05   $65.05   $65.00  
  Purchase #4 $51.50   10.793%   $57.0584   $57.06   $57.05   $57.10  
  Purchase #5 $47.67   7.272%   $51.1366   $51.14   $51.15   $51.10  
  Purchase #6 $197.27   4.854%   $206.8455   $206.85   $206.85   $206.80  
  Purchase #7 $240.89   3.754%   $249.933   $249.93   $249.95   $249.90  
  7 purchase totals = $955.56       $1,034.7751   $1,034.79   $1,034.80   $1,034.60