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 $78.39   12.364%   $88.0821   $88.08   $88.10   $88.10  
  Purchase #2 $82.64   4.334%   $86.2216   $86.22   $86.20   $86.20  
  Purchase #3 $96.39   5.342%   $101.5392   $101.54   $101.55   $101.50  
  Purchase #4 $60.27   13.461%   $68.3829   $68.38   $68.40   $68.40  
  Purchase #5 $246.56   6.719%   $263.1264   $263.13   $263.15   $263.10  
  Purchase #6 $149.41   11.712%   $166.9089   $166.91   $166.90   $166.90  
  Purchase #7 $80.99   4.168%   $84.3657   $84.37   $84.35   $84.40  
  7 purchase totals = $794.65       $858.6268   $858.63   $858.65   $858.60