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 $58.46   4.788%   $61.2591   $61.26   $61.25   $61.30  
  Purchase #2 $12.96   3.418%   $13.403   $13.40   $13.40   $13.40  
  Purchase #3 $242.89   8.301%   $263.0523   $263.05   $263.05   $263.10  
  Purchase #4 $77.32   7.330%   $82.9876   $82.99   $83.00   $83.00  
  Purchase #5 $207.53   12.674%   $233.8324   $233.83   $233.85   $233.80  
  Purchase #6 $191.71   8.460%   $207.9287   $207.93   $207.95   $207.90  
  Purchase #7 $136.51   9.348%   $149.271   $149.27   $149.25   $149.30  
  7 purchase totals = $927.38       $1,011.7341   $1,011.73   $1,011.75   $1,011.80