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 $204.86   13.828%   $233.188   $233.19   $233.20   $233.20  
  Purchase #2 $40.46   7.797%   $43.6147   $43.61   $43.60   $43.60  
  Purchase #3 $46.62   3.103%   $48.0666   $48.07   $48.05   $48.10  
  Purchase #4 $231.45   4.808%   $242.5781   $242.58   $242.60   $242.60  
  Purchase #5 $195.74   10.506%   $216.3044   $216.30   $216.30   $216.30  
  Purchase #6 $16.34   12.168%   $18.3283   $18.33   $18.35   $18.30  
  Purchase #7 $212.80   7.815%   $229.4303   $229.43   $229.45   $229.40  
  7 purchase totals = $948.27       $1,031.5104   $1,031.51   $1,031.55   $1,031.50