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 $49.43   6.368%   $52.5777   $52.58   $52.60   $52.60  
  Purchase #2 $128.48   11.852%   $143.7074   $143.71   $143.70   $143.70  
  Purchase #3 $207.73   3.605%   $215.2187   $215.22   $215.20   $215.20  
  Purchase #4 $137.61   3.674%   $142.6658   $142.67   $142.65   $142.70  
  Purchase #5 $103.79   8.492%   $112.6038   $112.60   $112.60   $112.60  
  Purchase #6 $134.36   3.210%   $138.673   $138.67   $138.65   $138.70  
  Purchase #7 $180.64   8.307%   $195.6458   $195.65   $195.65   $195.60  
  7 purchase totals = $942.04       $1,001.0922   $1,001.10   $1,001.05   $1,001.10