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 $63.87   5.353%   $67.289   $67.29   $67.30   $67.30  
  Purchase #2 $145.41   5.775%   $153.8074   $153.81   $153.80   $153.80  
  Purchase #3 $201.63   10.133%   $222.0612   $222.06   $222.05   $222.10  
  Purchase #4 $50.88   5.361%   $53.6077   $53.61   $53.60   $53.60  
  Purchase #5 $228.60   8.272%   $247.5098   $247.51   $247.50   $247.50  
  Purchase #6 $75.62   8.696%   $82.1959   $82.20   $82.20   $82.20  
  Purchase #7 $199.63   11.832%   $223.2502   $223.25   $223.25   $223.30  
  7 purchase totals = $965.64       $1,049.7212   $1,049.73   $1,049.70   $1,049.80