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 $34.93   9.813%   $38.3577   $38.36   $38.35   $38.40  
  Purchase #2 $108.96   7.281%   $116.8934   $116.89   $116.90   $116.90  
  Purchase #3 $65.38   4.431%   $68.277   $68.28   $68.30   $68.30  
  Purchase #4 $198.32   8.798%   $215.7682   $215.77   $215.75   $215.80  
  Purchase #5 $164.45   4.697%   $172.1742   $172.17   $172.15   $172.20  
  Purchase #6 $241.73   9.755%   $265.3108   $265.31   $265.30   $265.30  
  Purchase #7 $178.38   5.280%   $187.7985   $187.80   $187.80   $187.80  
  7 purchase totals = $992.15       $1,064.5798   $1,064.58   $1,064.55   $1,064.70