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 $211.96   5.325%   $223.2469   $223.25   $223.25   $223.20  
  Purchase #2 $120.30   3.534%   $124.5514   $124.55   $124.55   $124.60  
  Purchase #3 $248.75   7.459%   $267.3043   $267.30   $267.30   $267.30  
  Purchase #4 $37.90   13.282%   $42.9339   $42.93   $42.95   $42.90  
  Purchase #5 $125.87   12.105%   $141.1066   $141.11   $141.10   $141.10  
  Purchase #6 $229.46   4.731%   $240.3158   $240.32   $240.30   $240.30  
  Purchase #7 $24.94   7.456%   $26.7995   $26.80   $26.80   $26.80  
  7 purchase totals = $999.18       $1,066.2584   $1,066.26   $1,066.25   $1,066.20