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 $192.96   6.660%   $205.8111   $205.81   $205.80   $205.80  
  Purchase #2 $140.89   6.344%   $149.8281   $149.83   $149.85   $149.80  
  Purchase #3 $153.93   13.810%   $175.1877   $175.19   $175.20   $175.20  
  Purchase #4 $170.40   11.456%   $189.921   $189.92   $189.90   $189.90  
  Purchase #5 $181.76   9.203%   $198.4874   $198.49   $198.50   $198.50  
  Purchase #6 $15.60   6.410%   $16.6   $16.60   $16.60   $16.60  
  Purchase #7 $96.27   12.627%   $108.426   $108.43   $108.45   $108.40  
  7 purchase totals = $951.81       $1,044.2613   $1,044.27   $1,044.30   $1,044.20