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 $173.37   13.197%   $196.2496   $196.25   $196.25   $196.20  
  Purchase #2 $202.35   13.546%   $229.7603   $229.76   $229.75   $229.80  
  Purchase #3 $10.87   13.502%   $12.3377   $12.34   $12.35   $12.30  
  Purchase #4 $149.37   11.646%   $166.7656   $166.77   $166.75   $166.80  
  Purchase #5 $236.40   5.151%   $248.577   $248.58   $248.60   $248.60  
  Purchase #6 $225.75   11.657%   $252.0657   $252.07   $252.05   $252.10  
  Purchase #7 $80.93   5.545%   $85.4176   $85.42   $85.40   $85.40  
  7 purchase totals = $1,079.04       $1,191.1735   $1,191.19   $1,191.15   $1,191.20