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 $214.99   6.604%   $229.1879   $229.19   $229.20   $229.20  
  Purchase #2 $147.41   4.187%   $153.5821   $153.58   $153.60   $153.60  
  Purchase #3 $25.45   13.458%   $28.8751   $28.88   $28.90   $28.90  
  Purchase #4 $72.45   11.138%   $80.5195   $80.52   $80.50   $80.50  
  Purchase #5 $183.79   11.293%   $204.5454   $204.55   $204.55   $204.50  
  Purchase #6 $79.61   9.127%   $86.876   $86.88   $86.90   $86.90  
  Purchase #7 $232.69   3.301%   $240.3711   $240.37   $240.35   $240.40  
  7 purchase totals = $956.39       $1,023.9571   $1,023.97   $1,024.00   $1,024.00