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 $28.40   12.250%   $31.879   $31.88   $31.90   $31.90  
  Purchase #2 $116.54   3.269%   $120.3497   $120.35   $120.35   $120.30  
  Purchase #3 $38.82   6.447%   $41.3227   $41.32   $41.30   $41.30  
  Purchase #4 $161.44   5.591%   $170.4661   $170.47   $170.45   $170.50  
  Purchase #5 $8.34   4.744%   $8.7356   $8.74   $8.75   $8.70  
  Purchase #6 $167.84   4.806%   $175.9064   $175.91   $175.90   $175.90  
  Purchase #7 $136.26   8.347%   $147.6336   $147.63   $147.65   $147.60  
  7 purchase totals = $657.64       $696.2931   $696.30   $696.30   $696.20