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 $248.30   8.337%   $269.0008   $269.00   $269.00   $269.00  
  Purchase #2 $11.88   10.236%   $13.096   $13.10   $13.10   $13.10  
  Purchase #3 $16.41   6.667%   $17.5041   $17.50   $17.50   $17.50  
  Purchase #4 $70.27   10.378%   $77.5626   $77.56   $77.55   $77.60  
  Purchase #5 $187.51   12.548%   $211.0388   $211.04   $211.05   $211.00  
  Purchase #6 $243.64   11.366%   $271.3321   $271.33   $271.35   $271.30  
  Purchase #7 $103.73   4.193%   $108.0794   $108.08   $108.10   $108.10  
  7 purchase totals = $881.74       $967.6138   $967.61   $967.65   $967.60