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 $52.66   13.508%   $59.7733   $59.77   $59.75   $59.80  
  Purchase #2 $247.70   3.802%   $257.1176   $257.12   $257.10   $257.10  
  Purchase #3 $24.57   3.326%   $25.3872   $25.39   $25.40   $25.40  
  Purchase #4 $157.58   3.375%   $162.8983   $162.90   $162.90   $162.90  
  Purchase #5 $204.73   10.481%   $226.1878   $226.19   $226.20   $226.20  
  Purchase #6 $207.53   3.771%   $215.356   $215.36   $215.35   $215.40  
  Purchase #7 $223.81   10.640%   $247.6234   $247.62   $247.60   $247.60  
  7 purchase totals = $1,118.58       $1,194.3436   $1,194.35   $1,194.30   $1,194.40