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 $59.87   3.172%   $61.7691   $61.77   $61.75   $61.80  
  Purchase #2 $12.59   11.186%   $13.9983   $14.00   $14.00   $14.00  
  Purchase #3 $153.39   3.131%   $158.1926   $158.19   $158.20   $158.20  
  Purchase #4 $21.98   13.831%   $25.0201   $25.02   $25.00   $25.00  
  Purchase #5 $193.80   6.842%   $207.0598   $207.06   $207.05   $207.10  
  Purchase #6 $5.26   11.641%   $5.8723   $5.87   $5.85   $5.90  
  Purchase #7 $85.65   5.142%   $90.0541   $90.05   $90.05   $90.10  
  7 purchase totals = $532.54       $561.9663   $561.96   $561.90   $562.10