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 $57.52   3.171%   $59.344   $59.34   $59.35   $59.30  
  Purchase #2 $162.98   3.283%   $168.3306   $168.33   $168.35   $168.30  
  Purchase #3 $54.60   6.261%   $58.0185   $58.02   $58.00   $58.00  
  Purchase #4 $107.72   8.662%   $117.0507   $117.05   $117.05   $117.10  
  Purchase #5 $248.62   7.208%   $266.5405   $266.54   $266.55   $266.50  
  Purchase #6 $199.25   7.774%   $214.7397   $214.74   $214.75   $214.70  
  Purchase #7 $72.89   11.397%   $81.1973   $81.20   $81.20   $81.20  
  7 purchase totals = $903.58       $965.2213   $965.22   $965.25   $965.10