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 $139.56   7.202%   $149.6111   $149.61   $149.60   $149.60  
  Purchase #2 $133.81   5.844%   $141.6299   $141.63   $141.65   $141.60  
  Purchase #3 $247.25   13.765%   $281.284   $281.28   $281.30   $281.30  
  Purchase #4 $43.47   12.222%   $48.7829   $48.78   $48.80   $48.80  
  Purchase #5 $41.48   5.328%   $43.6901   $43.69   $43.70   $43.70  
  Purchase #6 $49.56   3.282%   $51.1866   $51.19   $51.20   $51.20  
  Purchase #7 $223.93   6.153%   $237.7084   $237.71   $237.70   $237.70  
  7 purchase totals = $879.06       $953.8930   $953.89   $953.95   $953.90