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 $226.41   9.412%   $247.7197   $247.72   $247.70   $247.70  
  Purchase #2 $238.88   5.284%   $251.5024   $251.50   $251.50   $251.50  
  Purchase #3 $166.75   8.121%   $180.2918   $180.29   $180.30   $180.30  
  Purchase #4 $129.51   3.243%   $133.71   $133.71   $133.70   $133.70  
  Purchase #5 $86.63   4.523%   $90.5483   $90.55   $90.55   $90.50  
  Purchase #6 $164.26   11.427%   $183.03   $183.03   $183.05   $183.00  
  Purchase #7 $161.85   3.798%   $167.9971   $168.00   $168.00   $168.00  
  7 purchase totals = $1,174.29       $1,254.7993   $1,254.80   $1,254.80   $1,254.70