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 $95.69   11.487%   $106.6819   $106.68   $106.70   $106.70  
  Purchase #2 $24.56   8.174%   $26.5675   $26.57   $26.55   $26.60  
  Purchase #3 $59.94   12.814%   $67.6207   $67.62   $67.60   $67.60  
  Purchase #4 $208.34   7.645%   $224.2676   $224.27   $224.25   $224.30  
  Purchase #5 $36.39   9.784%   $39.9504   $39.95   $39.95   $40.00  
  Purchase #6 $33.30   10.463%   $36.7842   $36.78   $36.80   $36.80  
  Purchase #7 $200.51   6.136%   $212.8133   $212.81   $212.80   $212.80  
  7 purchase totals = $658.73       $714.6856   $714.68   $714.65   $714.80