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 $84.30   3.262%   $87.0499   $87.05   $87.05   $87.00  
  Purchase #2 $209.85   11.149%   $233.2462   $233.25   $233.25   $233.20  
  Purchase #3 $229.35   5.156%   $241.1753   $241.18   $241.20   $241.20  
  Purchase #4 $77.30   10.687%   $85.5611   $85.56   $85.55   $85.60  
  Purchase #5 $6.70   11.527%   $7.4723   $7.47   $7.45   $7.50  
  Purchase #6 $15.61   4.360%   $16.2906   $16.29   $16.30   $16.30  
  Purchase #7 $147.70   4.441%   $154.2594   $154.26   $154.25   $154.30  
  7 purchase totals = $770.81       $825.0548   $825.06   $825.05   $825.10