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 $61.80   4.717%   $64.7151   $64.72   $64.70   $64.70  
  Purchase #2 $220.77   8.841%   $240.2883   $240.29   $240.30   $240.30  
  Purchase #3 $165.63   8.104%   $179.0527   $179.05   $179.05   $179.10  
  Purchase #4 $173.70   4.730%   $181.916   $181.92   $181.90   $181.90  
  Purchase #5 $215.67   6.732%   $230.1889   $230.19   $230.20   $230.20  
  Purchase #6 $220.38   9.269%   $240.807   $240.81   $240.80   $240.80  
  Purchase #7 $66.34   5.511%   $69.996   $70.00   $70.00   $70.00  
  7 purchase totals = $1,124.29       $1,206.9640   $1,206.98   $1,206.95   $1,207.00