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 $216.94   13.258%   $245.7019   $245.70   $245.70   $245.70  
  Purchase #2 $130.85   3.334%   $135.2125   $135.21   $135.20   $135.20  
  Purchase #3 $49.64   12.463%   $55.8266   $55.83   $55.85   $55.80  
  Purchase #4 $241.57   5.433%   $254.6945   $254.69   $254.70   $254.70  
  Purchase #5 $143.74   9.242%   $157.0245   $157.02   $157.00   $157.00  
  Purchase #6 $200.65   5.691%   $212.069   $212.07   $212.05   $212.10  
  Purchase #7 $107.86   7.263%   $115.6939   $115.69   $115.70   $115.70  
  7 purchase totals = $1,091.25       $1,176.2229   $1,176.21   $1,176.20   $1,176.20