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 $235.82   10.783%   $261.2485   $261.25   $261.25   $261.20  
  Purchase #2 $72.70   13.251%   $82.3335   $82.33   $82.35   $82.30  
  Purchase #3 $88.42   6.536%   $94.1991   $94.20   $94.20   $94.20  
  Purchase #4 $111.33   4.478%   $116.3154   $116.32   $116.30   $116.30  
  Purchase #5 $46.47   8.727%   $50.5254   $50.53   $50.55   $50.50  
  Purchase #6 $58.68   13.536%   $66.6229   $66.62   $66.60   $66.60  
  Purchase #7 $142.93   7.775%   $154.0428   $154.04   $154.05   $154.00  
  7 purchase totals = $756.35       $825.2876   $825.29   $825.30   $825.10