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 $240.54   5.582%   $253.9669   $253.97   $253.95   $254.00  
  Purchase #2 $229.98   3.233%   $237.4153   $237.42   $237.40   $237.40  
  Purchase #3 $118.33   10.153%   $130.344   $130.34   $130.35   $130.30  
  Purchase #4 $90.42   5.801%   $95.6653   $95.67   $95.65   $95.70  
  Purchase #5 $161.77   13.821%   $184.1282   $184.13   $184.15   $184.10  
  Purchase #6 $242.51   12.450%   $272.7025   $272.70   $272.70   $272.70  
  Purchase #7 $150.79   7.175%   $161.6092   $161.61   $161.60   $161.60  
  7 purchase totals = $1,234.34       $1,335.8314   $1,335.84   $1,335.80   $1,335.80