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 $241.90   12.339%   $271.748   $271.75   $271.75   $271.70  
  Purchase #2 $173.79   8.194%   $188.0304   $188.03   $188.05   $188.00  
  Purchase #3 $202.96   10.845%   $224.971   $224.97   $224.95   $225.00  
  Purchase #4 $139.91   11.275%   $155.6849   $155.68   $155.70   $155.70  
  Purchase #5 $207.76   5.181%   $218.524   $218.52   $218.50   $218.50  
  Purchase #6 $238.25   10.846%   $264.0906   $264.09   $264.10   $264.10  
  Purchase #7 $118.60   4.682%   $124.1529   $124.15   $124.15   $124.20  
  7 purchase totals = $1,323.17       $1,447.2018   $1,447.19   $1,447.20   $1,447.20