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 $148.93   13.453%   $168.9656   $168.97   $168.95   $169.00  
  Purchase #2 $101.90   8.634%   $110.698   $110.70   $110.70   $110.70  
  Purchase #3 $165.92   4.820%   $173.9173   $173.92   $173.90   $173.90  
  Purchase #4 $106.72   3.129%   $110.0593   $110.06   $110.05   $110.10  
  Purchase #5 $192.83   8.698%   $209.6024   $209.60   $209.60   $209.60  
  Purchase #6 $24.61   5.325%   $25.9205   $25.92   $25.90   $25.90  
  Purchase #7 $64.38   6.509%   $68.5705   $68.57   $68.55   $68.60  
  7 purchase totals = $805.29       $867.7336   $867.74   $867.65   $867.80