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 $23.42   12.184%   $26.2735   $26.27   $26.25   $26.30  
  Purchase #2 $148.66   9.352%   $162.5627   $162.56   $162.55   $162.60  
  Purchase #3 $187.56   13.243%   $212.3986   $212.40   $212.40   $212.40  
  Purchase #4 $143.76   5.654%   $151.8882   $151.89   $151.90   $151.90  
  Purchase #5 $162.82   13.238%   $184.3741   $184.37   $184.35   $184.40  
  Purchase #6 $210.81   9.459%   $230.7505   $230.75   $230.75   $230.80  
  Purchase #7 $34.36   9.727%   $37.7022   $37.70   $37.70   $37.70  
  7 purchase totals = $911.39       $1,005.9498   $1,005.94   $1,005.90   $1,006.10