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 $114.47   6.815%   $122.2711   $122.27   $122.25   $122.30  
  Purchase #2 $200.87   8.694%   $218.3336   $218.33   $218.35   $218.30  
  Purchase #3 $23.46   7.836%   $25.2983   $25.30   $25.30   $25.30  
  Purchase #4 $223.83   8.842%   $243.621   $243.62   $243.60   $243.60  
  Purchase #5 $224.34   11.549%   $250.249   $250.25   $250.25   $250.20  
  Purchase #6 $223.74   10.749%   $247.7898   $247.79   $247.80   $247.80  
  Purchase #7 $141.48   8.237%   $153.1337   $153.13   $153.15   $153.10  
  7 purchase totals = $1,152.19       $1,260.6965   $1,260.69   $1,260.70   $1,260.60