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 $203.96   3.779%   $211.6676   $211.67   $211.65   $211.70  
  Purchase #2 $51.83   13.114%   $58.627   $58.63   $58.65   $58.60  
  Purchase #3 $24.57   10.229%   $27.0833   $27.08   $27.10   $27.10  
  Purchase #4 $78.59   7.319%   $84.342   $84.34   $84.35   $84.30  
  Purchase #5 $220.43   5.636%   $232.8534   $232.85   $232.85   $232.90  
  Purchase #6 $151.50   12.119%   $169.8603   $169.86   $169.85   $169.90  
  Purchase #7 $81.48   5.775%   $86.1855   $86.19   $86.20   $86.20  
  7 purchase totals = $812.36       $870.6191   $870.62   $870.65   $870.70