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 $245.73   11.230%   $273.3255   $273.33   $273.35   $273.30  
  Purchase #2 $160.29   12.116%   $179.7107   $179.71   $179.70   $179.70  
  Purchase #3 $188.55   6.677%   $201.1395   $201.14   $201.15   $201.10  
  Purchase #4 $97.88   11.780%   $109.4103   $109.41   $109.40   $109.40  
  Purchase #5 $212.50   12.850%   $239.8063   $239.81   $239.80   $239.80  
  Purchase #6 $157.74   6.138%   $167.4221   $167.42   $167.40   $167.40  
  Purchase #7 $24.98   10.372%   $27.5709   $27.57   $27.55   $27.60  
  7 purchase totals = $1,087.67       $1,198.3853   $1,198.39   $1,198.35   $1,198.30