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 $56.46   7.294%   $60.5782   $60.58   $60.60   $60.60  
  Purchase #2 $140.96   10.588%   $155.8848   $155.88   $155.90   $155.90  
  Purchase #3 $45.63   7.751%   $49.1668   $49.17   $49.15   $49.20  
  Purchase #4 $246.28   8.503%   $267.2212   $267.22   $267.20   $267.20  
  Purchase #5 $50.74   9.763%   $55.6937   $55.69   $55.70   $55.70  
  Purchase #6 $105.56   6.195%   $112.0994   $112.10   $112.10   $112.10  
  Purchase #7 $181.63   3.307%   $187.6365   $187.64   $187.65   $187.60  
  7 purchase totals = $827.26       $888.2806   $888.28   $888.30   $888.30