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 $199.98   3.115%   $206.2094   $206.21   $206.20   $206.20  
  Purchase #2 $93.31   4.587%   $97.5901   $97.59   $97.60   $97.60  
  Purchase #3 $155.82   9.158%   $170.09   $170.09   $170.10   $170.10  
  Purchase #4 $158.36   8.459%   $171.7557   $171.76   $171.75   $171.80  
  Purchase #5 $233.95   5.519%   $246.8617   $246.86   $246.85   $246.90  
  Purchase #6 $250.72   6.129%   $266.0866   $266.09   $266.10   $266.10  
  Purchase #7 $226.72   5.420%   $239.0082   $239.01   $239.00   $239.00  
  7 purchase totals = $1,318.86       $1,397.6017   $1,397.61   $1,397.60   $1,397.70