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 $68.61   9.590%   $75.1897   $75.19   $75.20   $75.20  
  Purchase #2 $23.69   13.165%   $26.8088   $26.81   $26.80   $26.80  
  Purchase #3 $179.44   3.621%   $185.9375   $185.94   $185.95   $185.90  
  Purchase #4 $146.58   11.416%   $163.3136   $163.31   $163.30   $163.30  
  Purchase #5 $24.72   3.863%   $25.6749   $25.67   $25.65   $25.70  
  Purchase #6 $32.94   13.247%   $37.3036   $37.30   $37.30   $37.30  
  Purchase #7 $243.72   13.588%   $276.8367   $276.84   $276.85   $276.80  
  7 purchase totals = $719.70       $791.0648   $791.06   $791.05   $791.00