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 $67.53   6.290%   $71.7776   $71.78   $71.80   $71.80  
  Purchase #2 $73.58   11.255%   $81.8614   $81.86   $81.85   $81.90  
  Purchase #3 $159.77   4.837%   $167.4981   $167.50   $167.50   $167.50  
  Purchase #4 $204.58   6.280%   $217.4276   $217.43   $217.45   $217.40  
  Purchase #5 $229.93   6.828%   $245.6296   $245.63   $245.65   $245.60  
  Purchase #6 $234.93   13.797%   $267.3433   $267.34   $267.35   $267.30  
  Purchase #7 $214.51   7.673%   $230.9694   $230.97   $230.95   $231.00  
  7 purchase totals = $1,184.83       $1,282.5070   $1,282.51   $1,282.55   $1,282.50