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 $96.74   12.455%   $108.789   $108.79   $108.80   $108.80  
  Purchase #2 $168.55   12.751%   $190.0418   $190.04   $190.05   $190.00  
  Purchase #3 $155.47   12.843%   $175.437   $175.44   $175.45   $175.40  
  Purchase #4 $75.67   13.615%   $85.9725   $85.97   $85.95   $86.00  
  Purchase #5 $82.57   4.435%   $86.232   $86.23   $86.25   $86.20  
  Purchase #6 $157.56   12.334%   $176.9935   $176.99   $177.00   $177.00  
  Purchase #7 $170.83   11.127%   $189.8383   $189.84   $189.85   $189.80  
  7 purchase totals = $907.39       $1,013.3041   $1,013.30   $1,013.35   $1,013.20