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 $186.74   9.352%   $204.2039   $204.20   $204.20   $204.20  
  Purchase #2 $109.72   8.855%   $119.4357   $119.44   $119.45   $119.40  
  Purchase #3 $39.40   6.116%   $41.8097   $41.81   $41.80   $41.80  
  Purchase #4 $77.25   11.163%   $85.8734   $85.87   $85.85   $85.90  
  Purchase #5 $152.60   5.454%   $160.9228   $160.92   $160.90   $160.90  
  Purchase #6 $10.46   10.847%   $11.5946   $11.59   $11.60   $11.60  
  Purchase #7 $106.96   11.409%   $119.1631   $119.16   $119.15   $119.20  
  7 purchase totals = $683.13       $743.0032   $742.99   $742.95   $743.00