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 $156.56   7.685%   $168.5916   $168.59   $168.60   $168.60  
  Purchase #2 $103.68   12.705%   $116.8525   $116.85   $116.85   $116.90  
  Purchase #3 $214.67   9.305%   $234.645   $234.65   $234.65   $234.60  
  Purchase #4 $146.45   4.435%   $152.9451   $152.95   $152.95   $152.90  
  Purchase #5 $180.87   9.366%   $197.8103   $197.81   $197.80   $197.80  
  Purchase #6 $217.39   7.371%   $233.4138   $233.41   $233.40   $233.40  
  Purchase #7 $117.40   9.631%   $128.7068   $128.71   $128.70   $128.70  
  7 purchase totals = $1,137.02       $1,232.9651   $1,232.97   $1,232.95   $1,232.90