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 $24.70   8.174%   $26.719   $26.72   $26.70   $26.70  
  Purchase #2 $40.51   13.760%   $46.0842   $46.08   $46.10   $46.10  
  Purchase #3 $44.72   9.832%   $49.1169   $49.12   $49.10   $49.10  
  Purchase #4 $181.27   5.783%   $191.7528   $191.75   $191.75   $191.80  
  Purchase #5 $75.72   10.764%   $83.8705   $83.87   $83.85   $83.90  
  Purchase #6 $207.62   3.110%   $214.077   $214.08   $214.10   $214.10  
  Purchase #7 $86.47   11.463%   $96.3821   $96.38   $96.40   $96.40  
  7 purchase totals = $661.01       $708.0025   $708.00   $708.00   $708.10