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 $119.60   12.531%   $134.5871   $134.59   $134.60   $134.60  
  Purchase #2 $226.39   3.133%   $233.4828   $233.48   $233.50   $233.50  
  Purchase #3 $146.95   10.147%   $161.861   $161.86   $161.85   $161.90  
  Purchase #4 $87.70   12.492%   $98.6555   $98.66   $98.65   $98.70  
  Purchase #5 $25.44   9.488%   $27.8537   $27.85   $27.85   $27.90  
  Purchase #6 $55.82   10.661%   $61.771   $61.77   $61.75   $61.80  
  Purchase #7 $244.35   13.453%   $277.2224   $277.22   $277.20   $277.20  
  7 purchase totals = $906.25       $995.4335   $995.43   $995.40   $995.60