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 $238.26   4.779%   $249.6464   $249.65   $249.65   $249.60  
  Purchase #2 $217.45   4.734%   $227.7441   $227.74   $227.75   $227.70  
  Purchase #3 $241.25   8.754%   $262.369   $262.37   $262.35   $262.40  
  Purchase #4 $56.77   8.284%   $61.4728   $61.47   $61.45   $61.50  
  Purchase #5 $235.44   6.414%   $250.5411   $250.54   $250.55   $250.50  
  Purchase #6 $46.91   10.768%   $51.9613   $51.96   $51.95   $52.00  
  Purchase #7 $22.82   12.403%   $25.6504   $25.65   $25.65   $25.70  
  7 purchase totals = $1,058.90       $1,129.3851   $1,129.38   $1,129.35   $1,129.40