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 $225.94   3.371%   $233.5564   $233.56   $233.55   $233.60  
  Purchase #2 $240.83   5.752%   $254.6825   $254.68   $254.70   $254.70  
  Purchase #3 $220.54   6.828%   $235.5985   $235.60   $235.60   $235.60  
  Purchase #4 $53.54   9.591%   $58.675   $58.68   $58.70   $58.70  
  Purchase #5 $167.50   12.555%   $188.5296   $188.53   $188.55   $188.50  
  Purchase #6 $137.77   13.847%   $156.847   $156.85   $156.85   $156.80  
  Purchase #7 $216.75   12.868%   $244.6414   $244.64   $244.65   $244.60  
  7 purchase totals = $1,262.87       $1,372.5304   $1,372.54   $1,372.60   $1,372.50