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 $214.51   13.159%   $242.7374   $242.74   $242.75   $242.70  
  Purchase #2 $162.67   12.173%   $182.4718   $182.47   $182.45   $182.50  
  Purchase #3 $246.62   9.803%   $270.7962   $270.80   $270.80   $270.80  
  Purchase #4 $48.93   6.838%   $52.2758   $52.28   $52.30   $52.30  
  Purchase #5 $233.43   13.319%   $264.5205   $264.52   $264.50   $264.50  
  Purchase #6 $73.93   10.330%   $81.567   $81.57   $81.55   $81.60  
  Purchase #7 $140.99   7.560%   $151.6488   $151.65   $151.65   $151.60  
  7 purchase totals = $1,121.08       $1,246.0175   $1,246.03   $1,246.00   $1,246.00