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 $55.36   10.581%   $61.2176   $61.22   $61.20   $61.20  
  Purchase #2 $243.61   7.151%   $261.0306   $261.03   $261.05   $261.00  
  Purchase #3 $155.92   5.514%   $164.5174   $164.52   $164.50   $164.50  
  Purchase #4 $192.74   9.674%   $211.3857   $211.39   $211.40   $211.40  
  Purchase #5 $234.80   10.744%   $260.0269   $260.03   $260.05   $260.00  
  Purchase #6 $204.39   8.536%   $221.8367   $221.84   $221.85   $221.80  
  Purchase #7 $64.90   6.407%   $69.0581   $69.06   $69.05   $69.10  
  7 purchase totals = $1,151.72       $1,249.0730   $1,249.09   $1,249.10   $1,249.00