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 $157.90   5.145%   $166.024   $166.02   $166.00   $166.00  
  Purchase #2 $12.98   9.257%   $14.1816   $14.18   $14.20   $14.20  
  Purchase #3 $32.53   8.518%   $35.3009   $35.30   $35.30   $35.30  
  Purchase #4 $124.45   9.199%   $135.8982   $135.90   $135.90   $135.90  
  Purchase #5 $163.61   8.594%   $177.6706   $177.67   $177.65   $177.70  
  Purchase #6 $199.66   3.240%   $206.129   $206.13   $206.15   $206.10  
  Purchase #7 $91.81   6.386%   $97.673   $97.67   $97.65   $97.70  
  7 purchase totals = $782.94       $832.8773   $832.87   $832.85   $832.90