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 $116.98   6.253%   $124.2948   $124.29   $124.30   $124.30  
  Purchase #2 $211.40   6.670%   $225.5004   $225.50   $225.50   $225.50  
  Purchase #3 $32.75   4.408%   $34.1936   $34.19   $34.20   $34.20  
  Purchase #4 $225.54   7.516%   $242.4916   $242.49   $242.50   $242.50  
  Purchase #5 $57.28   8.792%   $62.3161   $62.32   $62.30   $62.30  
  Purchase #6 $171.65   6.452%   $182.7249   $182.72   $182.70   $182.70  
  Purchase #7 $75.66   12.487%   $85.1077   $85.11   $85.10   $85.10  
  7 purchase totals = $891.26       $956.6291   $956.62   $956.60   $956.60