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 $201.92   11.833%   $225.8132   $225.81   $225.80   $225.80  
  Purchase #2 $87.59   10.409%   $96.7072   $96.71   $96.70   $96.70  
  Purchase #3 $191.86   4.778%   $201.0271   $201.03   $201.05   $201.00  
  Purchase #4 $39.64   4.845%   $41.5606   $41.56   $41.55   $41.60  
  Purchase #5 $73.49   9.245%   $80.2842   $80.28   $80.30   $80.30  
  Purchase #6 $59.34   5.680%   $62.7105   $62.71   $62.70   $62.70  
  Purchase #7 $211.71   12.775%   $238.756   $238.76   $238.75   $238.80  
  7 purchase totals = $865.55       $946.8588   $946.86   $946.85   $946.90