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 $209.41   5.693%   $221.3317   $221.33   $221.35   $221.30  
  Purchase #2 $222.71   3.855%   $231.2955   $231.30   $231.30   $231.30  
  Purchase #3 $61.85   7.299%   $66.3644   $66.36   $66.35   $66.40  
  Purchase #4 $157.92   5.119%   $166.0039   $166.00   $166.00   $166.00  
  Purchase #5 $223.40   8.338%   $242.0271   $242.03   $242.05   $242.00  
  Purchase #6 $135.76   12.323%   $152.4897   $152.49   $152.50   $152.50  
  Purchase #7 $122.86   6.464%   $130.8017   $130.80   $130.80   $130.80  
  7 purchase totals = $1,133.91       $1,210.3140   $1,210.31   $1,210.35   $1,210.30