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 $239.46   10.490%   $264.5794   $264.58   $264.60   $264.60  
  Purchase #2 $244.51   3.765%   $253.7158   $253.72   $253.70   $253.70  
  Purchase #3 $198.77   8.848%   $216.3572   $216.36   $216.35   $216.40  
  Purchase #4 $9.50   11.560%   $10.5982   $10.60   $10.60   $10.60  
  Purchase #5 $59.61   11.645%   $66.5516   $66.55   $66.55   $66.60  
  Purchase #6 $176.64   6.726%   $188.5208   $188.52   $188.50   $188.50  
  Purchase #7 $188.67   8.196%   $204.1334   $204.13   $204.15   $204.10  
  7 purchase totals = $1,117.16       $1,204.4564   $1,204.46   $1,204.45   $1,204.50