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 $204.43   4.792%   $214.2263   $214.23   $214.25   $214.20  
  Purchase #2 $7.26   10.337%   $8.0105   $8.01   $8.00   $8.00  
  Purchase #3 $211.64   9.249%   $231.2146   $231.21   $231.20   $231.20  
  Purchase #4 $24.59   12.265%   $27.606   $27.61   $27.60   $27.60  
  Purchase #5 $241.38   4.516%   $252.2807   $252.28   $252.30   $252.30  
  Purchase #6 $171.38   12.210%   $192.3055   $192.31   $192.30   $192.30  
  Purchase #7 $207.42   6.711%   $221.34   $221.34   $221.35   $221.30  
  7 purchase totals = $1,068.10       $1,146.9836   $1,146.99   $1,147.00   $1,146.90