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 $61.74   7.671%   $66.4761   $66.48   $66.50   $66.50  
  Purchase #2 $26.97   8.309%   $29.2109   $29.21   $29.20   $29.20  
  Purchase #3 $203.52   3.335%   $210.3074   $210.31   $210.30   $210.30  
  Purchase #4 $152.66   6.406%   $162.4394   $162.44   $162.45   $162.40  
  Purchase #5 $186.32   6.643%   $198.6972   $198.70   $198.70   $198.70  
  Purchase #6 $178.28   5.220%   $187.5862   $187.59   $187.60   $187.60  
  Purchase #7 $149.95   7.525%   $161.2337   $161.23   $161.25   $161.20  
  7 purchase totals = $959.44       $1,015.9509   $1,015.96   $1,016.00   $1,015.90