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 $112.77   10.607%   $124.7315   $124.73   $124.75   $124.70  
  Purchase #2 $65.45   8.441%   $70.9746   $70.97   $70.95   $71.00  
  Purchase #3 $159.61   13.574%   $181.2755   $181.28   $181.30   $181.30  
  Purchase #4 $246.71   9.318%   $269.6984   $269.70   $269.70   $269.70  
  Purchase #5 $210.86   10.635%   $233.285   $233.29   $233.30   $233.30  
  Purchase #6 $187.83   5.770%   $198.6678   $198.67   $198.65   $198.70  
  Purchase #7 $120.32   13.298%   $136.3202   $136.32   $136.30   $136.30  
  7 purchase totals = $1,103.55       $1,214.9530   $1,214.96   $1,214.95   $1,215.00