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 $232.42   10.698%   $257.2843   $257.28   $257.30   $257.30  
  Purchase #2 $62.51   6.255%   $66.42   $66.42   $66.40   $66.40  
  Purchase #3 $19.37   4.636%   $20.268   $20.27   $20.25   $20.30  
  Purchase #4 $197.82   6.418%   $210.5161   $210.52   $210.50   $210.50  
  Purchase #5 $131.41   9.564%   $143.9781   $143.98   $144.00   $144.00  
  Purchase #6 $149.57   9.523%   $163.8136   $163.81   $163.80   $163.80  
  Purchase #7 $83.56   3.843%   $86.7712   $86.77   $86.75   $86.80  
  7 purchase totals = $876.66       $949.0513   $949.05   $949.00   $949.10