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 $200.26   12.793%   $225.8793   $225.88   $225.90   $225.90  
  Purchase #2 $159.43   4.465%   $166.5485   $166.55   $166.55   $166.50  
  Purchase #3 $204.94   8.174%   $221.6918   $221.69   $221.70   $221.70  
  Purchase #4 $149.97   12.177%   $168.2318   $168.23   $168.25   $168.20  
  Purchase #5 $60.37   6.788%   $64.4679   $64.47   $64.45   $64.50  
  Purchase #6 $149.96   3.808%   $155.6705   $155.67   $155.65   $155.70  
  Purchase #7 $10.39   13.593%   $11.8023   $11.80   $11.80   $11.80  
  7 purchase totals = $935.32       $1,014.2921   $1,014.29   $1,014.30   $1,014.30