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 $52.66   6.251%   $55.9518   $55.95   $55.95   $56.00  
  Purchase #2 $113.53   10.582%   $125.5437   $125.54   $125.55   $125.50  
  Purchase #3 $199.62   4.609%   $208.8205   $208.82   $208.80   $208.80  
  Purchase #4 $243.44   6.665%   $259.6653   $259.67   $259.65   $259.70  
  Purchase #5 $147.94   12.592%   $166.5686   $166.57   $166.55   $166.60  
  Purchase #6 $21.27   11.429%   $23.7009   $23.70   $23.70   $23.70  
  Purchase #7 $5.32   10.147%   $5.8598   $5.86   $5.85   $5.90  
  7 purchase totals = $783.78       $846.1106   $846.11   $846.05   $846.20