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 $56.32   5.344%   $59.3297   $59.33   $59.35   $59.30  
  Purchase #2 $25.65   3.470%   $26.5401   $26.54   $26.55   $26.50  
  Purchase #3 $197.57   9.322%   $215.9875   $215.99   $216.00   $216.00  
  Purchase #4 $241.84   12.665%   $272.469   $272.47   $272.45   $272.50  
  Purchase #5 $177.26   11.499%   $197.6431   $197.64   $197.65   $197.60  
  Purchase #6 $15.90   7.536%   $17.0982   $17.10   $17.10   $17.10  
  Purchase #7 $169.95   5.773%   $179.7612   $179.76   $179.75   $179.80  
  7 purchase totals = $884.49       $968.8288   $968.83   $968.85   $968.80