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 $220.58   6.207%   $234.2714   $234.27   $234.25   $234.30  
  Purchase #2 $116.65   10.114%   $128.448   $128.45   $128.45   $128.40  
  Purchase #3 $26.32   10.312%   $29.0341   $29.03   $29.05   $29.00  
  Purchase #4 $242.59   8.556%   $263.346   $263.35   $263.35   $263.30  
  Purchase #5 $36.29   8.476%   $39.3659   $39.37   $39.35   $39.40  
  Purchase #6 $134.81   9.702%   $147.8893   $147.89   $147.90   $147.90  
  Purchase #7 $178.69   8.383%   $193.6696   $193.67   $193.65   $193.70  
  7 purchase totals = $955.93       $1,036.0243   $1,036.03   $1,036.00   $1,036.00