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 $209.61   5.129%   $220.3609   $220.36   $220.35   $220.40  
  Purchase #2 $8.81   10.209%   $9.7094   $9.71   $9.70   $9.70  
  Purchase #3 $119.70   5.259%   $125.995   $126.00   $126.00   $126.00  
  Purchase #4 $178.45   4.807%   $187.0281   $187.03   $187.05   $187.00  
  Purchase #5 $27.67   4.789%   $28.9951   $29.00   $29.00   $29.00  
  Purchase #6 $130.85   9.509%   $143.2925   $143.29   $143.30   $143.30  
  Purchase #7 $114.52   11.461%   $127.6451   $127.65   $127.65   $127.60  
  7 purchase totals = $789.61       $843.0261   $843.04   $843.05   $843.00