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 $58.53   3.417%   $60.53   $60.53   $60.55   $60.50  
  Purchase #2 $10.63   8.689%   $11.5536   $11.55   $11.55   $11.60  
  Purchase #3 $249.53   9.151%   $272.3645   $272.36   $272.35   $272.40  
  Purchase #4 $127.26   5.740%   $134.5647   $134.56   $134.55   $134.60  
  Purchase #5 $10.28   13.184%   $11.6353   $11.64   $11.65   $11.60  
  Purchase #6 $166.71   6.552%   $177.6328   $177.63   $177.65   $177.60  
  Purchase #7 $159.29   8.607%   $173.0001   $173.00   $173.00   $173.00  
  7 purchase totals = $782.23       $841.2810   $841.27   $841.30   $841.30