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 $16.29   8.310%   $17.6437   $17.64   $17.65   $17.60  
  Purchase #2 $59.92   12.335%   $67.3111   $67.31   $67.30   $67.30  
  Purchase #3 $207.66   5.247%   $218.5559   $218.56   $218.55   $218.60  
  Purchase #4 $141.52   12.683%   $159.469   $159.47   $159.45   $159.50  
  Purchase #5 $73.98   9.767%   $81.2056   $81.21   $81.20   $81.20  
  Purchase #6 $94.77   11.524%   $105.6913   $105.69   $105.70   $105.70  
  Purchase #7 $236.78   4.659%   $247.8116   $247.81   $247.80   $247.80  
  7 purchase totals = $830.92       $897.6882   $897.69   $897.65   $897.70