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 $185.97   10.874%   $206.1924   $206.19   $206.20   $206.20  
  Purchase #2 $70.39   6.306%   $74.8288   $74.83   $74.85   $74.80  
  Purchase #3 $92.73   9.642%   $101.671   $101.67   $101.65   $101.70  
  Purchase #4 $187.77   3.257%   $193.8857   $193.89   $193.90   $193.90  
  Purchase #5 $71.82   13.680%   $81.645   $81.65   $81.65   $81.60  
  Purchase #6 $224.88   11.870%   $251.5733   $251.57   $251.55   $251.60  
  Purchase #7 $175.43   12.484%   $197.3307   $197.33   $197.35   $197.30  
  7 purchase totals = $1,008.99       $1,107.1269   $1,107.13   $1,107.15   $1,107.10