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 $240.25   8.643%   $261.0148   $261.01   $261.00   $261.00  
  Purchase #2 $64.52   3.119%   $66.5324   $66.53   $66.55   $66.50  
  Purchase #3 $62.92   13.138%   $71.1864   $71.19   $71.20   $71.20  
  Purchase #4 $175.95   6.614%   $187.5873   $187.59   $187.60   $187.60  
  Purchase #5 $69.91   9.430%   $76.5025   $76.50   $76.50   $76.50  
  Purchase #6 $45.48   3.431%   $47.0404   $47.04   $47.05   $47.00  
  Purchase #7 $52.74   12.353%   $59.255   $59.26   $59.25   $59.30  
  7 purchase totals = $711.77       $769.1188   $769.12   $769.15   $769.10