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 $62.84   6.128%   $66.6908   $66.69   $66.70   $66.70  
  Purchase #2 $106.67   13.748%   $121.335   $121.34   $121.35   $121.30  
  Purchase #3 $164.56   6.627%   $175.4654   $175.47   $175.45   $175.50  
  Purchase #4 $26.95   8.798%   $29.3211   $29.32   $29.30   $29.30  
  Purchase #5 $217.60   10.850%   $241.2096   $241.21   $241.20   $241.20  
  Purchase #6 $164.27   12.406%   $184.6493   $184.65   $184.65   $184.60  
  Purchase #7 $180.71   9.697%   $198.2334   $198.23   $198.25   $198.20  
  7 purchase totals = $923.60       $1,016.9046   $1,016.91   $1,016.90   $1,016.80