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 $96.32   6.671%   $102.7455   $102.75   $102.75   $102.70  
  Purchase #2 $126.31   9.158%   $137.8775   $137.88   $137.90   $137.90  
  Purchase #3 $155.71   8.857%   $169.5012   $169.50   $169.50   $169.50  
  Purchase #4 $66.69   7.826%   $71.9092   $71.91   $71.90   $71.90  
  Purchase #5 $69.36   12.656%   $78.1382   $78.14   $78.15   $78.10  
  Purchase #6 $106.93   13.504%   $121.3698   $121.37   $121.35   $121.40  
  Purchase #7 $86.44   9.866%   $94.9682   $94.97   $94.95   $95.00  
  7 purchase totals = $707.76       $776.5096   $776.52   $776.50   $776.50