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 $115.36   10.177%   $127.1002   $127.10   $127.10   $127.10  
  Purchase #2 $215.34   12.363%   $241.9625   $241.96   $241.95   $242.00  
  Purchase #3 $26.41   8.421%   $28.634   $28.63   $28.65   $28.60  
  Purchase #4 $149.82   5.369%   $157.8638   $157.86   $157.85   $157.90  
  Purchase #5 $241.90   9.565%   $265.0377   $265.04   $265.05   $265.00  
  Purchase #6 $115.98   10.379%   $128.0176   $128.02   $128.00   $128.00  
  Purchase #7 $31.92   4.436%   $33.336   $33.34   $33.35   $33.30  
  7 purchase totals = $896.73       $981.9518   $981.95   $981.95   $981.90