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 $201.80   6.496%   $214.9089   $214.91   $214.90   $214.90  
  Purchase #2 $240.42   7.260%   $257.8745   $257.87   $257.85   $257.90  
  Purchase #3 $120.86   9.256%   $132.0468   $132.05   $132.05   $132.00  
  Purchase #4 $230.83   5.391%   $243.274   $243.27   $243.25   $243.30  
  Purchase #5 $69.82   13.199%   $79.0355   $79.04   $79.05   $79.00  
  Purchase #6 $37.32   9.511%   $40.8695   $40.87   $40.85   $40.90  
  Purchase #7 $120.29   11.691%   $134.3531   $134.35   $134.35   $134.40  
  7 purchase totals = $1,021.34       $1,102.3623   $1,102.36   $1,102.30   $1,102.40