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 $208.30   12.193%   $233.698   $233.70   $233.70   $233.70  
  Purchase #2 $18.42   7.484%   $19.7986   $19.80   $19.80   $19.80  
  Purchase #3 $86.90   4.837%   $91.1034   $91.10   $91.10   $91.10  
  Purchase #4 $213.95   3.731%   $221.9325   $221.93   $221.95   $221.90  
  Purchase #5 $246.84   12.800%   $278.4355   $278.44   $278.45   $278.40  
  Purchase #6 $154.86   10.632%   $171.3247   $171.32   $171.30   $171.30  
  Purchase #7 $193.84   3.317%   $200.2697   $200.27   $200.25   $200.30  
  7 purchase totals = $1,123.11       $1,216.5624   $1,216.56   $1,216.55   $1,216.50