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 $96.76   5.156%   $101.7489   $101.75   $101.75   $101.70  
  Purchase #2 $228.79   11.616%   $255.3662   $255.37   $255.35   $255.40  
  Purchase #3 $99.36   6.369%   $105.6882   $105.69   $105.70   $105.70  
  Purchase #4 $220.63   4.751%   $231.1121   $231.11   $231.10   $231.10  
  Purchase #5 $99.88   13.679%   $113.5426   $113.54   $113.55   $113.50  
  Purchase #6 $95.72   10.810%   $106.0673   $106.07   $106.05   $106.10  
  Purchase #7 $208.73   11.727%   $233.2078   $233.21   $233.20   $233.20  
  7 purchase totals = $1,049.87       $1,146.7331   $1,146.74   $1,146.70   $1,146.70