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 $217.41   7.350%   $233.3896   $233.39   $233.40   $233.40  
  Purchase #2 $28.72   4.436%   $29.994   $29.99   $30.00   $30.00  
  Purchase #3 $12.89   8.266%   $13.9555   $13.96   $13.95   $14.00  
  Purchase #4 $27.41   13.453%   $31.0975   $31.10   $31.10   $31.10  
  Purchase #5 $21.80   8.222%   $23.5924   $23.59   $23.60   $23.60  
  Purchase #6 $111.48   5.269%   $117.3539   $117.35   $117.35   $117.40  
  Purchase #7 $79.75   9.458%   $87.2928   $87.29   $87.30   $87.30  
  7 purchase totals = $499.46       $536.6757   $536.67   $536.70   $536.80