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 $207.66   10.598%   $229.6678   $229.67   $229.65   $229.70  
  Purchase #2 $159.59   9.502%   $174.7542   $174.75   $174.75   $174.80  
  Purchase #3 $228.74   3.473%   $236.6841   $236.68   $236.70   $236.70  
  Purchase #4 $38.74   9.774%   $42.5264   $42.53   $42.55   $42.50  
  Purchase #5 $150.60   3.576%   $155.9855   $155.99   $156.00   $156.00  
  Purchase #6 $226.34   3.655%   $234.6127   $234.61   $234.60   $234.60  
  Purchase #7 $223.87   13.211%   $253.4455   $253.45   $253.45   $253.40  
  7 purchase totals = $1,235.54       $1,327.6762   $1,327.68   $1,327.70   $1,327.70