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 $84.53   8.289%   $91.5367   $91.54   $91.55   $91.50  
  Purchase #2 $81.58   12.357%   $91.6608   $91.66   $91.65   $91.70  
  Purchase #3 $58.99   5.159%   $62.0333   $62.03   $62.05   $62.00  
  Purchase #4 $191.95   11.595%   $214.2066   $214.21   $214.20   $214.20  
  Purchase #5 $234.60   11.698%   $262.0435   $262.04   $262.05   $262.00  
  Purchase #6 $92.60   3.505%   $95.8456   $95.85   $95.85   $95.80  
  Purchase #7 $192.66   8.549%   $209.1305   $209.13   $209.15   $209.10  
  7 purchase totals = $936.91       $1,026.4570   $1,026.46   $1,026.50   $1,026.30