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 $26.74   6.294%   $28.423   $28.42   $28.40   $28.40  
  Purchase #2 $160.71   11.514%   $179.2141   $179.21   $179.20   $179.20  
  Purchase #3 $198.52   13.732%   $225.7808   $225.78   $225.80   $225.80  
  Purchase #4 $39.79   12.342%   $44.7009   $44.70   $44.70   $44.70  
  Purchase #5 $94.44   12.522%   $106.2658   $106.27   $106.25   $106.30  
  Purchase #6 $22.36   6.676%   $23.8528   $23.85   $23.85   $23.90  
  Purchase #7 $196.36   12.820%   $221.5334   $221.53   $221.55   $221.50  
  7 purchase totals = $738.92       $829.7708   $829.76   $829.75   $829.80