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 $179.26   12.301%   $201.3108   $201.31   $201.30   $201.30  
  Purchase #2 $97.55   6.560%   $103.9493   $103.95   $103.95   $103.90  
  Purchase #3 $178.74   8.757%   $194.3923   $194.39   $194.40   $194.40  
  Purchase #4 $198.44   11.685%   $221.6277   $221.63   $221.65   $221.60  
  Purchase #5 $120.53   10.785%   $133.5292   $133.53   $133.55   $133.50  
  Purchase #6 $19.73   10.233%   $21.749   $21.75   $21.75   $21.70  
  Purchase #7 $203.97   11.187%   $226.7881   $226.79   $226.80   $226.80  
  7 purchase totals = $998.22       $1,103.3464   $1,103.35   $1,103.40   $1,103.20