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 $81.81   13.164%   $92.5795   $92.58   $92.60   $92.60  
  Purchase #2 $183.35   7.731%   $197.5248   $197.52   $197.50   $197.50  
  Purchase #3 $103.61   4.619%   $108.3957   $108.40   $108.40   $108.40  
  Purchase #4 $40.99   8.650%   $44.5356   $44.54   $44.55   $44.50  
  Purchase #5 $142.44   13.497%   $161.6651   $161.67   $161.65   $161.70  
  Purchase #6 $196.48   13.512%   $223.0284   $223.03   $223.05   $223.00  
  Purchase #7 $101.56   3.748%   $105.3665   $105.37   $105.35   $105.40  
  7 purchase totals = $850.24       $933.0956   $933.11   $933.10   $933.10