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 $83.71   11.826%   $93.6095   $93.61   $93.60   $93.60  
  Purchase #2 $218.62   13.357%   $247.8211   $247.82   $247.80   $247.80  
  Purchase #3 $214.55   6.463%   $228.4164   $228.42   $228.40   $228.40  
  Purchase #4 $210.72   10.574%   $233.0015   $233.00   $233.00   $233.00  
  Purchase #5 $34.48   11.824%   $38.5569   $38.56   $38.55   $38.60  
  Purchase #6 $245.50   13.118%   $277.7047   $277.70   $277.70   $277.70  
  Purchase #7 $235.53   10.744%   $260.8353   $260.84   $260.85   $260.80  
  7 purchase totals = $1,243.11       $1,379.9454   $1,379.95   $1,379.90   $1,379.90