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 $214.83   13.557%   $243.9545   $243.95   $243.95   $244.00  
  Purchase #2 $111.61   12.393%   $125.4418   $125.44   $125.45   $125.40  
  Purchase #3 $159.37   9.499%   $174.5086   $174.51   $174.50   $174.50  
  Purchase #4 $137.28   5.549%   $144.8977   $144.90   $144.90   $144.90  
  Purchase #5 $24.97   3.549%   $25.8562   $25.86   $25.85   $25.90  
  Purchase #6 $65.69   5.270%   $69.1519   $69.15   $69.15   $69.20  
  Purchase #7 $120.71   5.438%   $127.2742   $127.27   $127.25   $127.30  
  7 purchase totals = $834.46       $911.0849   $911.08   $911.05   $911.20