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 $246.75   6.856%   $263.6672   $263.67   $263.65   $263.70  
  Purchase #2 $74.79   3.829%   $77.6537   $77.65   $77.65   $77.70  
  Purchase #3 $50.47   5.507%   $53.2494   $53.25   $53.25   $53.20  
  Purchase #4 $188.55   13.841%   $214.6472   $214.65   $214.65   $214.60  
  Purchase #5 $115.62   5.414%   $121.8797   $121.88   $121.90   $121.90  
  Purchase #6 $180.45   3.846%   $187.3901   $187.39   $187.40   $187.40  
  Purchase #7 $84.75   13.133%   $95.8802   $95.88   $95.90   $95.90  
  7 purchase totals = $941.38       $1,014.3675   $1,014.37   $1,014.40   $1,014.40