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 $243.28   7.202%   $260.801   $260.80   $260.80   $260.80  
  Purchase #2 $227.80   6.361%   $242.2904   $242.29   $242.30   $242.30  
  Purchase #3 $56.97   12.673%   $64.1898   $64.19   $64.20   $64.20  
  Purchase #4 $240.55   9.668%   $263.8064   $263.81   $263.80   $263.80  
  Purchase #5 $51.84   11.142%   $57.616   $57.62   $57.60   $57.60  
  Purchase #6 $11.36   9.713%   $12.4634   $12.46   $12.45   $12.50  
  Purchase #7 $157.44   10.715%   $174.3097   $174.31   $174.30   $174.30  
  7 purchase totals = $989.24       $1,075.4767   $1,075.48   $1,075.45   $1,075.50