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 $102.96   6.763%   $109.9232   $109.92   $109.90   $109.90  
  Purchase #2 $175.35   11.308%   $195.1786   $195.18   $195.20   $195.20  
  Purchase #3 $214.31   12.112%   $240.2672   $240.27   $240.25   $240.30  
  Purchase #4 $179.54   7.624%   $193.2281   $193.23   $193.25   $193.20  
  Purchase #5 $186.27   13.547%   $211.504   $211.50   $211.50   $211.50  
  Purchase #6 $29.97   11.587%   $33.4426   $33.44   $33.45   $33.40  
  Purchase #7 $64.86   9.413%   $70.9653   $70.97   $70.95   $71.00  
  7 purchase totals = $953.26       $1,054.5090   $1,054.51   $1,054.50   $1,054.50