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 $54.62   5.623%   $57.6913   $57.69   $57.70   $57.70  
  Purchase #2 $142.34   13.384%   $161.3908   $161.39   $161.40   $161.40  
  Purchase #3 $167.34   11.280%   $186.216   $186.22   $186.20   $186.20  
  Purchase #4 $239.79   11.503%   $267.373   $267.37   $267.35   $267.40  
  Purchase #5 $123.52   10.458%   $136.4377   $136.44   $136.45   $136.40  
  Purchase #6 $184.34   8.347%   $199.7269   $199.73   $199.75   $199.70  
  Purchase #7 $190.64   8.279%   $206.4231   $206.42   $206.40   $206.40  
  7 purchase totals = $1,102.59       $1,215.2588   $1,215.26   $1,215.25   $1,215.20