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 $111.51   13.294%   $126.3341   $126.33   $126.35   $126.30  
  Purchase #2 $204.42   6.380%   $217.462   $217.46   $217.45   $217.50  
  Purchase #3 $69.73   3.230%   $71.9823   $71.98   $72.00   $72.00  
  Purchase #4 $44.41   9.837%   $48.7786   $48.78   $48.80   $48.80  
  Purchase #5 $164.60   7.142%   $176.3557   $176.36   $176.35   $176.40  
  Purchase #6 $181.70   4.280%   $189.4768   $189.48   $189.50   $189.50  
  Purchase #7 $23.57   4.509%   $24.6328   $24.63   $24.65   $24.60  
  7 purchase totals = $799.94       $855.0223   $855.02   $855.10   $855.10