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 $60.59   4.208%   $63.1396   $63.14   $63.15   $63.10  
  Purchase #2 $151.32   8.415%   $164.0536   $164.05   $164.05   $164.10  
  Purchase #3 $32.52   13.508%   $36.9128   $36.91   $36.90   $36.90  
  Purchase #4 $197.30   8.496%   $214.0626   $214.06   $214.05   $214.10  
  Purchase #5 $100.97   7.667%   $108.7114   $108.71   $108.70   $108.70  
  Purchase #6 $23.89   13.637%   $27.1479   $27.15   $27.15   $27.10  
  Purchase #7 $152.96   6.639%   $163.115   $163.12   $163.10   $163.10  
  7 purchase totals = $719.55       $777.1429   $777.14   $777.10   $777.10