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 $53.58   10.596%   $59.2573   $59.26   $59.25   $59.30  
  Purchase #2 $148.41   5.117%   $156.0041   $156.00   $156.00   $156.00  
  Purchase #3 $204.65   3.183%   $211.164   $211.16   $211.15   $211.20  
  Purchase #4 $10.76   8.782%   $11.7049   $11.70   $11.70   $11.70  
  Purchase #5 $31.78   12.513%   $35.7566   $35.76   $35.75   $35.80  
  Purchase #6 $34.84   7.642%   $37.5025   $37.50   $37.50   $37.50  
  Purchase #7 $131.65   6.868%   $140.6917   $140.69   $140.70   $140.70  
  7 purchase totals = $615.67       $652.0811   $652.07   $652.05   $652.20