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 $52.88   10.590%   $58.48   $58.48   $58.50   $58.50  
  Purchase #2 $65.28   8.302%   $70.6995   $70.70   $70.70   $70.70  
  Purchase #3 $174.78   3.695%   $181.2381   $181.24   $181.25   $181.20  
  Purchase #4 $171.43   7.319%   $183.977   $183.98   $184.00   $184.00  
  Purchase #5 $111.95   13.485%   $127.0465   $127.05   $127.05   $127.00  
  Purchase #6 $192.99   4.123%   $200.947   $200.95   $200.95   $200.90  
  Purchase #7 $17.82   4.547%   $18.6303   $18.63   $18.65   $18.60  
  7 purchase totals = $787.13       $841.0184   $841.03   $841.10   $840.90