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 $23.53   13.260%   $26.6501   $26.65   $26.65   $26.70  
  Purchase #2 $98.94   10.146%   $108.9785   $108.98   $109.00   $109.00  
  Purchase #3 $175.96   13.466%   $199.6548   $199.65   $199.65   $199.70  
  Purchase #4 $222.40   4.164%   $231.6607   $231.66   $231.65   $231.70  
  Purchase #5 $26.38   11.709%   $29.4688   $29.47   $29.45   $29.50  
  Purchase #6 $186.40   10.428%   $205.8378   $205.84   $205.85   $205.80  
  Purchase #7 $184.78   3.870%   $191.931   $191.93   $191.95   $191.90  
  7 purchase totals = $918.39       $994.1817   $994.18   $994.20   $994.30