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 $96.88   10.758%   $107.3024   $107.30   $107.30   $107.30  
  Purchase #2 $176.44   7.794%   $190.1917   $190.19   $190.20   $190.20  
  Purchase #3 $16.70   13.246%   $18.9121   $18.91   $18.90   $18.90  
  Purchase #4 $229.36   4.583%   $239.8716   $239.87   $239.85   $239.90  
  Purchase #5 $97.30   7.152%   $104.2589   $104.26   $104.25   $104.30  
  Purchase #6 $121.50   11.392%   $135.3413   $135.34   $135.35   $135.30  
  Purchase #7 $203.65   12.309%   $228.7173   $228.72   $228.70   $228.70  
  7 purchase totals = $941.83       $1,024.5953   $1,024.59   $1,024.55   $1,024.60