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 $235.74   10.723%   $261.0184   $261.02   $261.00   $261.00  
  Purchase #2 $222.97   4.548%   $233.1107   $233.11   $233.10   $233.10  
  Purchase #3 $202.52   11.701%   $226.2169   $226.22   $226.20   $226.20  
  Purchase #4 $35.70   11.261%   $39.7202   $39.72   $39.70   $39.70  
  Purchase #5 $148.71   5.623%   $157.072   $157.07   $157.05   $157.10  
  Purchase #6 $45.51   8.678%   $49.4594   $49.46   $49.45   $49.50  
  Purchase #7 $104.46   5.160%   $109.8501   $109.85   $109.85   $109.90  
  7 purchase totals = $995.61       $1,076.4477   $1,076.45   $1,076.35   $1,076.50