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 $44.79   12.690%   $50.4739   $50.47   $50.45   $50.50  
  Purchase #2 $181.92   10.131%   $200.3503   $200.35   $200.35   $200.40  
  Purchase #3 $32.33   12.486%   $36.3667   $36.37   $36.35   $36.40  
  Purchase #4 $39.29   8.791%   $42.744   $42.74   $42.75   $42.70  
  Purchase #5 $201.58   12.164%   $226.1002   $226.10   $226.10   $226.10  
  Purchase #6 $105.30   12.465%   $118.4256   $118.43   $118.45   $118.40  
  Purchase #7 $215.48   8.799%   $234.4401   $234.44   $234.45   $234.40  
  7 purchase totals = $820.69       $908.9008   $908.90   $908.90   $908.90