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 $76.43   13.373%   $86.651   $86.65   $86.65   $86.70  
  Purchase #2 $44.53   6.601%   $47.4694   $47.47   $47.45   $47.50  
  Purchase #3 $71.32   11.497%   $79.5197   $79.52   $79.50   $79.50  
  Purchase #4 $214.62   3.319%   $221.7432   $221.74   $221.75   $221.70  
  Purchase #5 $243.32   6.717%   $259.6638   $259.66   $259.65   $259.70  
  Purchase #6 $164.72   7.133%   $176.4695   $176.47   $176.45   $176.50  
  Purchase #7 $51.30   9.418%   $56.1314   $56.13   $56.15   $56.10  
  7 purchase totals = $866.24       $927.6480   $927.64   $927.60   $927.70