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 $143.65   12.108%   $161.0431   $161.04   $161.05   $161.00  
  Purchase #2 $179.90   13.205%   $203.6558   $203.66   $203.65   $203.70  
  Purchase #3 $101.29   8.813%   $110.2167   $110.22   $110.20   $110.20  
  Purchase #4 $14.40   9.589%   $15.7808   $15.78   $15.80   $15.80  
  Purchase #5 $151.75   6.721%   $161.9491   $161.95   $161.95   $161.90  
  Purchase #6 $99.45   8.726%   $108.128   $108.13   $108.15   $108.10  
  Purchase #7 $103.84   11.233%   $115.5043   $115.50   $115.50   $115.50  
  7 purchase totals = $794.28       $876.2778   $876.28   $876.30   $876.20