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 $38.83   10.757%   $43.0069   $43.01   $43.00   $43.00  
  Purchase #2 $148.63   12.824%   $167.6903   $167.69   $167.70   $167.70  
  Purchase #3 $131.77   11.148%   $146.4597   $146.46   $146.45   $146.50  
  Purchase #4 $47.54   6.617%   $50.6857   $50.69   $50.70   $50.70  
  Purchase #5 $222.30   6.505%   $236.7606   $236.76   $236.75   $236.80  
  Purchase #6 $183.50   10.403%   $202.5895   $202.59   $202.60   $202.60  
  Purchase #7 $246.48   5.690%   $260.5047   $260.50   $260.50   $260.50  
  7 purchase totals = $1,019.05       $1,107.6974   $1,107.70   $1,107.70   $1,107.80