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 $218.84   9.540%   $239.7173   $239.72   $239.70   $239.70  
  Purchase #2 $204.83   3.710%   $212.4292   $212.43   $212.45   $212.40  
  Purchase #3 $97.90   12.766%   $110.3979   $110.40   $110.40   $110.40  
  Purchase #4 $192.53   12.370%   $216.346   $216.35   $216.35   $216.30  
  Purchase #5 $32.83   4.781%   $34.3996   $34.40   $34.40   $34.40  
  Purchase #6 $199.32   8.697%   $216.6549   $216.65   $216.65   $216.70  
  Purchase #7 $170.47   8.502%   $184.9634   $184.96   $184.95   $185.00  
  7 purchase totals = $1,116.72       $1,214.9083   $1,214.91   $1,214.90   $1,214.90