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 $245.94   10.796%   $272.4917   $272.49   $272.50   $272.50  
  Purchase #2 $222.51   4.574%   $232.6876   $232.69   $232.70   $232.70  
  Purchase #3 $151.39   12.447%   $170.2335   $170.23   $170.25   $170.20  
  Purchase #4 $188.92   6.664%   $201.5096   $201.51   $201.50   $201.50  
  Purchase #5 $206.58   8.264%   $223.6518   $223.65   $223.65   $223.70  
  Purchase #6 $65.35   3.210%   $67.4477   $67.45   $67.45   $67.40  
  Purchase #7 $178.93   13.176%   $202.5058   $202.51   $202.50   $202.50  
  7 purchase totals = $1,259.62       $1,370.5277   $1,370.53   $1,370.55   $1,370.50