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 $48.58   4.193%   $50.617   $50.62   $50.60   $50.60  
  Purchase #2 $194.52   3.201%   $200.7466   $200.75   $200.75   $200.70  
  Purchase #3 $214.61   13.209%   $242.9578   $242.96   $242.95   $243.00  
  Purchase #4 $128.63   5.122%   $135.2184   $135.22   $135.20   $135.20  
  Purchase #5 $34.85   7.874%   $37.5941   $37.59   $37.60   $37.60  
  Purchase #6 $59.74   11.852%   $66.8204   $66.82   $66.80   $66.80  
  Purchase #7 $134.38   8.582%   $145.9125   $145.91   $145.90   $145.90  
  7 purchase totals = $815.31       $879.8668   $879.87   $879.80   $879.80