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 $68.37   12.838%   $77.1473   $77.15   $77.15   $77.10  
  Purchase #2 $84.52   13.384%   $95.8322   $95.83   $95.85   $95.80  
  Purchase #3 $87.37   6.445%   $93.001   $93.00   $93.00   $93.00  
  Purchase #4 $27.86   12.336%   $31.2968   $31.30   $31.30   $31.30  
  Purchase #5 $82.27   10.227%   $90.6838   $90.68   $90.70   $90.70  
  Purchase #6 $208.78   8.264%   $226.0336   $226.03   $226.05   $226.00  
  Purchase #7 $227.77   7.776%   $245.4814   $245.48   $245.50   $245.50  
  7 purchase totals = $786.94       $859.4761   $859.47   $859.55   $859.40