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 $88.76   8.184%   $96.0241   $96.02   $96.00   $96.00  
  Purchase #2 $246.78   7.488%   $265.2589   $265.26   $265.25   $265.30  
  Purchase #3 $43.75   12.631%   $49.2761   $49.28   $49.30   $49.30  
  Purchase #4 $8.74   10.735%   $9.6782   $9.68   $9.70   $9.70  
  Purchase #5 $37.75   3.828%   $39.1951   $39.20   $39.20   $39.20  
  Purchase #6 $118.33   5.830%   $125.2286   $125.23   $125.25   $125.20  
  Purchase #7 $14.86   9.393%   $16.2558   $16.26   $16.25   $16.30  
  7 purchase totals = $558.97       $600.9168   $600.93   $600.95   $601.00