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 $62.56   8.791%   $68.0596   $68.06   $68.05   $68.10  
  Purchase #2 $99.94   13.160%   $113.0921   $113.09   $113.10   $113.10  
  Purchase #3 $239.70   12.817%   $270.4223   $270.42   $270.40   $270.40  
  Purchase #4 $194.63   5.108%   $204.5717   $204.57   $204.55   $204.60  
  Purchase #5 $221.88   5.418%   $233.9015   $233.90   $233.90   $233.90  
  Purchase #6 $172.54   3.647%   $178.8325   $178.83   $178.85   $178.80  
  Purchase #7 $127.68   10.515%   $141.1056   $141.11   $141.10   $141.10  
  7 purchase totals = $1,118.93       $1,209.9853   $1,209.98   $1,209.95   $1,210.00