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 $22.94   8.311%   $24.8465   $24.85   $24.85   $24.80  
  Purchase #2 $155.51   10.556%   $171.9256   $171.93   $171.95   $171.90  
  Purchase #3 $186.87   12.423%   $210.0849   $210.08   $210.10   $210.10  
  Purchase #4 $91.36   3.344%   $94.4151   $94.42   $94.40   $94.40  
  Purchase #5 $89.93   4.317%   $93.8123   $93.81   $93.80   $93.80  
  Purchase #6 $202.54   3.432%   $209.4912   $209.49   $209.50   $209.50  
  Purchase #7 $243.92   3.704%   $252.9548   $252.95   $252.95   $253.00  
  7 purchase totals = $993.07       $1,057.5304   $1,057.53   $1,057.55   $1,057.50