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 $23.49   11.143%   $26.1075   $26.11   $26.10   $26.10  
  Purchase #2 $113.86   7.330%   $122.2059   $122.21   $122.20   $122.20  
  Purchase #3 $47.90   7.668%   $51.573   $51.57   $51.55   $51.60  
  Purchase #4 $156.43   11.744%   $174.8011   $174.80   $174.80   $174.80  
  Purchase #5 $9.35   11.672%   $10.4413   $10.44   $10.45   $10.40  
  Purchase #6 $8.34   9.869%   $9.1631   $9.16   $9.15   $9.20  
  Purchase #7 $157.29   5.404%   $165.79   $165.79   $165.80   $165.80  
  7 purchase totals = $516.66       $560.0819   $560.08   $560.05   $560.10