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 $92.26   12.282%   $103.5914   $103.59   $103.60   $103.60  
  Purchase #2 $24.28   7.409%   $26.0789   $26.08   $26.10   $26.10  
  Purchase #3 $192.44   10.281%   $212.2248   $212.22   $212.20   $212.20  
  Purchase #4 $122.37   4.488%   $127.862   $127.86   $127.85   $127.90  
  Purchase #5 $112.76   11.608%   $125.8492   $125.85   $125.85   $125.80  
  Purchase #6 $242.64   8.417%   $263.063   $263.06   $263.05   $263.10  
  Purchase #7 $132.72   4.703%   $138.9618   $138.96   $138.95   $139.00  
  7 purchase totals = $919.47       $997.6311   $997.62   $997.60   $997.70