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 $91.99   3.517%   $95.2253   $95.23   $95.25   $95.20  
  Purchase #2 $216.78   13.255%   $245.5142   $245.51   $245.50   $245.50  
  Purchase #3 $161.55   12.549%   $181.8229   $181.82   $181.80   $181.80  
  Purchase #4 $213.84   9.585%   $234.3366   $234.34   $234.35   $234.30  
  Purchase #5 $5.33   9.356%   $5.8287   $5.83   $5.85   $5.80  
  Purchase #6 $141.26   13.151%   $159.8371   $159.84   $159.85   $159.80  
  Purchase #7 $7.60   13.243%   $8.6065   $8.61   $8.60   $8.60  
  7 purchase totals = $838.35       $931.1713   $931.18   $931.20   $931.00