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 $77.39   12.243%   $86.8649   $86.86   $86.85   $86.90  
  Purchase #2 $15.71   5.608%   $16.591   $16.59   $16.60   $16.60  
  Purchase #3 $213.37   5.317%   $224.7149   $224.71   $224.70   $224.70  
  Purchase #4 $195.81   12.564%   $220.4116   $220.41   $220.40   $220.40  
  Purchase #5 $202.62   10.506%   $223.9073   $223.91   $223.90   $223.90  
  Purchase #6 $61.77   5.159%   $64.9567   $64.96   $64.95   $65.00  
  Purchase #7 $162.93   3.492%   $168.6195   $168.62   $168.60   $168.60  
  7 purchase totals = $929.60       $1,006.0659   $1,006.06   $1,006.00   $1,006.10