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 $49.93   9.767%   $54.8067   $54.81   $54.80   $54.80  
  Purchase #2 $77.68   13.852%   $88.4402   $88.44   $88.45   $88.40  
  Purchase #3 $86.74   9.194%   $94.7149   $94.71   $94.70   $94.70  
  Purchase #4 $145.73   7.763%   $157.043   $157.04   $157.05   $157.00  
  Purchase #5 $174.35   11.831%   $194.9773   $194.98   $195.00   $195.00  
  Purchase #6 $176.58   13.469%   $200.3636   $200.36   $200.35   $200.40  
  Purchase #7 $191.96   12.472%   $215.9013   $215.90   $215.90   $215.90  
  7 purchase totals = $902.97       $1,006.2470   $1,006.24   $1,006.25   $1,006.20