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 $56.51   10.312%   $62.3373   $62.34   $62.35   $62.30  
  Purchase #2 $46.85   8.616%   $50.8866   $50.89   $50.90   $50.90  
  Purchase #3 $173.90   10.330%   $191.8639   $191.86   $191.85   $191.90  
  Purchase #4 $223.74   8.475%   $242.702   $242.70   $242.70   $242.70  
  Purchase #5 $80.79   6.782%   $86.2692   $86.27   $86.25   $86.30  
  Purchase #6 $70.95   8.186%   $76.758   $76.76   $76.75   $76.80  
  Purchase #7 $52.52   4.246%   $54.75   $54.75   $54.75   $54.80  
  7 purchase totals = $705.26       $765.5670   $765.57   $765.55   $765.70