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 $195.82   5.608%   $206.8016   $206.80   $206.80   $206.80  
  Purchase #2 $206.44   11.107%   $229.3693   $229.37   $229.35   $229.40  
  Purchase #3 $117.86   4.155%   $122.7571   $122.76   $122.75   $122.80  
  Purchase #4 $26.37   3.347%   $27.2526   $27.25   $27.25   $27.30  
  Purchase #5 $134.62   3.701%   $139.6023   $139.60   $139.60   $139.60  
  Purchase #6 $97.91   13.599%   $111.2248   $111.22   $111.20   $111.20  
  Purchase #7 $149.50   10.117%   $164.6249   $164.62   $164.60   $164.60  
  7 purchase totals = $928.52       $1,001.6326   $1,001.62   $1,001.55   $1,001.70