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 $51.95   3.116%   $53.5688   $53.57   $53.55   $53.60  
  Purchase #2 $230.29   9.431%   $252.0086   $252.01   $252.00   $252.00  
  Purchase #3 $87.64   10.186%   $96.567   $96.57   $96.55   $96.60  
  Purchase #4 $44.32   4.797%   $46.446   $46.45   $46.45   $46.40  
  Purchase #5 $62.71   3.686%   $65.0215   $65.02   $65.00   $65.00  
  Purchase #6 $155.98   13.603%   $177.198   $177.20   $177.20   $177.20  
  Purchase #7 $72.65   10.467%   $80.2543   $80.25   $80.25   $80.30  
  7 purchase totals = $705.54       $771.0642   $771.07   $771.00   $771.10