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 $86.26   11.627%   $96.2895   $96.29   $96.30   $96.30  
  Purchase #2 $46.53   13.575%   $52.8464   $52.85   $52.85   $52.80  
  Purchase #3 $46.78   12.225%   $52.4989   $52.50   $52.50   $52.50  
  Purchase #4 $78.58   11.368%   $87.513   $87.51   $87.50   $87.50  
  Purchase #5 $162.90   3.780%   $169.0576   $169.06   $169.05   $169.10  
  Purchase #6 $124.68   6.119%   $132.3092   $132.31   $132.30   $132.30  
  Purchase #7 $239.51   3.158%   $247.0737   $247.07   $247.05   $247.10  
  7 purchase totals = $785.24       $837.5883   $837.59   $837.55   $837.60