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 $175.47   10.166%   $193.3083   $193.31   $193.30   $193.30  
  Purchase #2 $150.84   8.420%   $163.5407   $163.54   $163.55   $163.50  
  Purchase #3 $244.80   4.528%   $255.8845   $255.88   $255.90   $255.90  
  Purchase #4 $243.96   13.625%   $277.1996   $277.20   $277.20   $277.20  
  Purchase #5 $226.55   13.712%   $257.6145   $257.61   $257.60   $257.60  
  Purchase #6 $176.81   5.394%   $186.3471   $186.35   $186.35   $186.30  
  Purchase #7 $126.31   5.721%   $133.5362   $133.54   $133.55   $133.50  
  7 purchase totals = $1,344.74       $1,467.4309   $1,467.43   $1,467.45   $1,467.30