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 $86.41   10.279%   $95.2921   $95.29   $95.30   $95.30  
  Purchase #2 $82.62   12.249%   $92.7401   $92.74   $92.75   $92.70  
  Purchase #3 $180.65   11.292%   $201.049   $201.05   $201.05   $201.00  
  Purchase #4 $50.69   10.182%   $55.8513   $55.85   $55.85   $55.90  
  Purchase #5 $111.87   7.616%   $120.39   $120.39   $120.40   $120.40  
  Purchase #6 $128.91   9.688%   $141.3988   $141.40   $141.40   $141.40  
  Purchase #7 $117.32   8.162%   $126.8957   $126.90   $126.90   $126.90  
  7 purchase totals = $758.47       $833.6170   $833.62   $833.65   $833.60