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 $24.48   10.402%   $27.0264   $27.03   $27.05   $27.00  
  Purchase #2 $168.53   5.827%   $178.3502   $178.35   $178.35   $178.40  
  Purchase #3 $96.96   8.576%   $105.2753   $105.28   $105.30   $105.30  
  Purchase #4 $213.65   4.421%   $223.0955   $223.10   $223.10   $223.10  
  Purchase #5 $25.74   8.307%   $27.8782   $27.88   $27.90   $27.90  
  Purchase #6 $165.63   3.708%   $171.7716   $171.77   $171.75   $171.80  
  Purchase #7 $111.64   8.243%   $120.8425   $120.84   $120.85   $120.80  
  7 purchase totals = $806.63       $854.2397   $854.25   $854.30   $854.30