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 $89.51   4.591%   $93.6194   $93.62   $93.60   $93.60  
  Purchase #2 $243.79   13.329%   $276.2848   $276.28   $276.30   $276.30  
  Purchase #3 $38.43   4.556%   $40.1809   $40.18   $40.20   $40.20  
  Purchase #4 $237.95   12.205%   $266.9918   $266.99   $267.00   $267.00  
  Purchase #5 $180.37   5.823%   $190.8729   $190.87   $190.85   $190.90  
  Purchase #6 $174.86   8.434%   $189.6077   $189.61   $189.60   $189.60  
  Purchase #7 $68.79   8.540%   $74.6647   $74.66   $74.65   $74.70  
  7 purchase totals = $1,033.70       $1,132.2222   $1,132.21   $1,132.20   $1,132.30