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 $242.37   11.236%   $269.6027   $269.60   $269.60   $269.60  
  Purchase #2 $89.54   10.571%   $99.0053   $99.01   $99.00   $99.00  
  Purchase #3 $54.72   11.343%   $60.9269   $60.93   $60.95   $60.90  
  Purchase #4 $178.86   13.295%   $202.6394   $202.64   $202.65   $202.60  
  Purchase #5 $172.64   11.511%   $192.5126   $192.51   $192.50   $192.50  
  Purchase #6 $163.84   7.831%   $176.6703   $176.67   $176.65   $176.70  
  Purchase #7 $191.53   8.779%   $208.3444   $208.34   $208.35   $208.30  
  7 purchase totals = $1,093.50       $1,209.7016   $1,209.70   $1,209.70   $1,209.60