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 $60.53   9.536%   $66.3021   $66.30   $66.30   $66.30  
  Purchase #2 $186.42   7.629%   $200.642   $200.64   $200.65   $200.60  
  Purchase #3 $206.27   3.753%   $214.0113   $214.01   $214.00   $214.00  
  Purchase #4 $217.85   8.195%   $235.7028   $235.70   $235.70   $235.70  
  Purchase #5 $79.43   10.407%   $87.6963   $87.70   $87.70   $87.70  
  Purchase #6 $140.97   4.283%   $147.0077   $147.01   $147.00   $147.00  
  Purchase #7 $27.97   10.466%   $30.8973   $30.90   $30.90   $30.90  
  7 purchase totals = $919.44       $982.2595   $982.26   $982.25   $982.20