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 $240.73   3.691%   $249.6153   $249.62   $249.60   $249.60  
  Purchase #2 $212.46   12.457%   $238.9261   $238.93   $238.95   $238.90  
  Purchase #3 $22.98   12.462%   $25.8438   $25.84   $25.85   $25.80  
  Purchase #4 $22.96   7.491%   $24.6799   $24.68   $24.70   $24.70  
  Purchase #5 $229.68   5.328%   $241.9174   $241.92   $241.90   $241.90  
  Purchase #6 $236.57   12.172%   $265.3653   $265.37   $265.35   $265.40  
  Purchase #7 $106.29   9.217%   $116.0867   $116.09   $116.10   $116.10  
  7 purchase totals = $1,071.67       $1,162.4345   $1,162.45   $1,162.45   $1,162.40