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 $224.53   7.127%   $240.5323   $240.53   $240.55   $240.50  
  Purchase #2 $203.61   11.116%   $226.2433   $226.24   $226.25   $226.20  
  Purchase #3 $23.86   13.696%   $27.1279   $27.13   $27.15   $27.10  
  Purchase #4 $74.37   6.282%   $79.0419   $79.04   $79.05   $79.00  
  Purchase #5 $187.36   13.111%   $211.9248   $211.92   $211.90   $211.90  
  Purchase #6 $190.41   8.697%   $206.97   $206.97   $206.95   $207.00  
  Purchase #7 $66.97   7.656%   $72.0972   $72.10   $72.10   $72.10  
  7 purchase totals = $971.11       $1,063.9374   $1,063.93   $1,063.95   $1,063.80