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 $60.60   6.807%   $64.725   $64.73   $64.75   $64.70  
  Purchase #2 $75.90   10.325%   $83.7367   $83.74   $83.75   $83.70  
  Purchase #3 $16.30   11.588%   $18.1888   $18.19   $18.20   $18.20  
  Purchase #4 $205.88   11.372%   $229.2927   $229.29   $229.30   $229.30  
  Purchase #5 $120.81   4.793%   $126.6004   $126.60   $126.60   $126.60  
  Purchase #6 $186.43   8.314%   $201.9298   $201.93   $201.95   $201.90  
  Purchase #7 $200.64   10.266%   $221.2377   $221.24   $221.25   $221.20  
  7 purchase totals = $866.56       $945.7111   $945.72   $945.80   $945.60