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 $57.34   8.119%   $61.9954   $62.00   $62.00   $62.00  
  Purchase #2 $99.43   9.617%   $108.9922   $108.99   $109.00   $109.00  
  Purchase #3 $227.62   12.392%   $255.8267   $255.83   $255.85   $255.80  
  Purchase #4 $124.98   4.278%   $130.3266   $130.33   $130.35   $130.30  
  Purchase #5 $25.88   13.364%   $29.3386   $29.34   $29.35   $29.30  
  Purchase #6 $206.42   4.144%   $214.974   $214.97   $214.95   $215.00  
  Purchase #7 $182.25   12.361%   $204.7779   $204.78   $204.80   $204.80  
  7 purchase totals = $923.92       $1,006.2314   $1,006.24   $1,006.30   $1,006.20