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 $86.80   10.835%   $96.2048   $96.20   $96.20   $96.20  
  Purchase #2 $179.68   3.250%   $185.5196   $185.52   $185.50   $185.50  
  Purchase #3 $39.57   8.717%   $43.0193   $43.02   $43.00   $43.00  
  Purchase #4 $236.77   12.789%   $267.0505   $267.05   $267.05   $267.10  
  Purchase #5 $229.95   5.187%   $241.8775   $241.88   $241.90   $241.90  
  Purchase #6 $25.37   10.264%   $27.974   $27.97   $27.95   $28.00  
  Purchase #7 $33.88   3.195%   $34.9625   $34.96   $34.95   $35.00  
  7 purchase totals = $832.02       $896.6082   $896.60   $896.55   $896.70