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 $181.65   13.625%   $206.3998   $206.40   $206.40   $206.40  
  Purchase #2 $173.86   10.121%   $191.4564   $191.46   $191.45   $191.50  
  Purchase #3 $158.28   13.317%   $179.3581   $179.36   $179.35   $179.40  
  Purchase #4 $57.87   10.407%   $63.8925   $63.89   $63.90   $63.90  
  Purchase #5 $175.77   11.813%   $196.5337   $196.53   $196.55   $196.50  
  Purchase #6 $219.47   12.442%   $246.7765   $246.78   $246.80   $246.80  
  Purchase #7 $15.94   7.661%   $17.1612   $17.16   $17.15   $17.20  
  7 purchase totals = $982.84       $1,101.5782   $1,101.58   $1,101.60   $1,101.70