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 $239.29   10.572%   $264.5877   $264.59   $264.60   $264.60  
  Purchase #2 $117.39   6.459%   $124.9722   $124.97   $124.95   $125.00  
  Purchase #3 $163.45   3.746%   $169.5728   $169.57   $169.55   $169.60  
  Purchase #4 $138.57   8.633%   $150.5327   $150.53   $150.55   $150.50  
  Purchase #5 $163.26   3.202%   $168.4876   $168.49   $168.50   $168.50  
  Purchase #6 $119.48   4.135%   $124.4205   $124.42   $124.40   $124.40  
  Purchase #7 $115.81   5.498%   $122.1772   $122.18   $122.20   $122.20  
  7 purchase totals = $1,057.25       $1,124.7507   $1,124.75   $1,124.75   $1,124.80