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 $241.93   10.213%   $266.6383   $266.64   $266.65   $266.60  
  Purchase #2 $29.39   10.246%   $32.4013   $32.40   $32.40   $32.40  
  Purchase #3 $47.83   8.272%   $51.7865   $51.79   $51.80   $51.80  
  Purchase #4 $81.97   13.728%   $93.2228   $93.22   $93.20   $93.20  
  Purchase #5 $96.52   11.467%   $107.5879   $107.59   $107.60   $107.60  
  Purchase #6 $51.31   12.665%   $57.8084   $57.81   $57.80   $57.80  
  Purchase #7 $218.38   8.337%   $236.5863   $236.59   $236.60   $236.60  
  7 purchase totals = $767.33       $846.0315   $846.04   $846.05   $846.00