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 $61.75   6.612%   $65.8329   $65.83   $65.85   $65.80  
  Purchase #2 $49.75   5.472%   $52.4723   $52.47   $52.45   $52.50  
  Purchase #3 $105.52   9.720%   $115.7765   $115.78   $115.80   $115.80  
  Purchase #4 $238.82   4.809%   $250.3049   $250.30   $250.30   $250.30  
  Purchase #5 $149.63   8.147%   $161.8204   $161.82   $161.80   $161.80  
  Purchase #6 $107.49   5.675%   $113.5901   $113.59   $113.60   $113.60  
  Purchase #7 $23.67   6.181%   $25.133   $25.13   $25.15   $25.10  
  7 purchase totals = $736.63       $784.9301   $784.92   $784.95   $784.90