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 $36.66   8.561%   $39.7985   $39.80   $39.80   $39.80  
  Purchase #2 $228.51   5.561%   $241.2174   $241.22   $241.20   $241.20  
  Purchase #3 $209.59   13.249%   $237.3586   $237.36   $237.35   $237.40  
  Purchase #4 $213.71   7.335%   $229.3856   $229.39   $229.40   $229.40  
  Purchase #5 $45.87   10.106%   $50.5056   $50.51   $50.50   $50.50  
  Purchase #6 $213.46   13.651%   $242.5994   $242.60   $242.60   $242.60  
  Purchase #7 $153.65   4.809%   $161.039   $161.04   $161.05   $161.00  
  7 purchase totals = $1,101.45       $1,201.9041   $1,201.92   $1,201.90   $1,201.90