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 $218.68   12.863%   $246.8088   $246.81   $246.80   $246.80  
  Purchase #2 $187.85   8.292%   $203.4265   $203.43   $203.45   $203.40  
  Purchase #3 $101.65   6.153%   $107.9045   $107.90   $107.90   $107.90  
  Purchase #4 $38.32   8.447%   $41.5569   $41.56   $41.55   $41.60  
  Purchase #5 $194.84   10.175%   $214.665   $214.67   $214.65   $214.70  
  Purchase #6 $129.52   10.781%   $143.4836   $143.48   $143.50   $143.50  
  Purchase #7 $229.59   8.481%   $249.0615   $249.06   $249.05   $249.10  
  7 purchase totals = $1,100.45       $1,206.9068   $1,206.91   $1,206.90   $1,207.00