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 $85.37   8.809%   $92.8902   $92.89   $92.90   $92.90  
  Purchase #2 $95.82   6.397%   $101.9496   $101.95   $101.95   $101.90  
  Purchase #3 $200.67   9.284%   $219.3002   $219.30   $219.30   $219.30  
  Purchase #4 $198.54   10.443%   $219.2735   $219.27   $219.25   $219.30  
  Purchase #5 $53.29   13.840%   $60.6653   $60.67   $60.65   $60.70  
  Purchase #6 $178.77   5.147%   $187.9713   $187.97   $187.95   $188.00  
  Purchase #7 $154.35   6.704%   $164.6976   $164.70   $164.70   $164.70  
  7 purchase totals = $966.81       $1,046.7477   $1,046.75   $1,046.70   $1,046.80