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 $91.57   7.407%   $98.3526   $98.35   $98.35   $98.40  
  Purchase #2 $199.26   12.515%   $224.1974   $224.20   $224.20   $224.20  
  Purchase #3 $207.58   12.594%   $233.7226   $233.72   $233.70   $233.70  
  Purchase #4 $93.54   8.298%   $101.3019   $101.30   $101.30   $101.30  
  Purchase #5 $212.97   12.451%   $239.4869   $239.49   $239.50   $239.50  
  Purchase #6 $53.26   12.176%   $59.7449   $59.74   $59.75   $59.70  
  Purchase #7 $59.95   8.682%   $65.1549   $65.15   $65.15   $65.20  
  7 purchase totals = $918.13       $1,021.9612   $1,021.95   $1,021.95   $1,022.00