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 $216.78   5.453%   $228.601   $228.60   $228.60   $228.60  
  Purchase #2 $40.26   8.354%   $43.6233   $43.62   $43.60   $43.60  
  Purchase #3 $62.84   5.237%   $66.1309   $66.13   $66.15   $66.10  
  Purchase #4 $238.94   8.764%   $259.8807   $259.88   $259.90   $259.90  
  Purchase #5 $41.32   5.410%   $43.5554   $43.56   $43.55   $43.60  
  Purchase #6 $88.55   5.169%   $93.1271   $93.13   $93.15   $93.10  
  Purchase #7 $148.65   3.802%   $154.3017   $154.30   $154.30   $154.30  
  7 purchase totals = $837.34       $889.2201   $889.22   $889.25   $889.20