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 $197.74   5.656%   $208.9242   $208.92   $208.90   $208.90  
  Purchase #2 $163.45   13.614%   $185.7021   $185.70   $185.70   $185.70  
  Purchase #3 $117.54   7.208%   $126.0123   $126.01   $126.00   $126.00  
  Purchase #4 $27.63   10.396%   $30.5024   $30.50   $30.50   $30.50  
  Purchase #5 $37.78   9.504%   $41.3706   $41.37   $41.35   $41.40  
  Purchase #6 $170.60   10.391%   $188.327   $188.33   $188.35   $188.30  
  Purchase #7 $228.66   5.320%   $240.8247   $240.82   $240.80   $240.80  
  7 purchase totals = $943.40       $1,021.6633   $1,021.65   $1,021.60   $1,021.60