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 $44.27   12.853%   $49.96   $49.96   $49.95   $50.00  
  Purchase #2 $28.89   11.293%   $32.1525   $32.15   $32.15   $32.20  
  Purchase #3 $27.48   10.254%   $30.2978   $30.30   $30.30   $30.30  
  Purchase #4 $212.37   9.804%   $233.1908   $233.19   $233.20   $233.20  
  Purchase #5 $167.67   13.155%   $189.727   $189.73   $189.75   $189.70  
  Purchase #6 $213.66   5.129%   $224.6186   $224.62   $224.60   $224.60  
  Purchase #7 $220.94   6.489%   $235.2768   $235.28   $235.30   $235.30  
  7 purchase totals = $915.28       $995.2235   $995.23   $995.25   $995.30