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 $233.98   8.747%   $254.4462   $254.45   $254.45   $254.40  
  Purchase #2 $136.32   12.493%   $153.3505   $153.35   $153.35   $153.40  
  Purchase #3 $230.52   9.643%   $252.749   $252.75   $252.75   $252.70  
  Purchase #4 $36.47   12.698%   $41.101   $41.10   $41.10   $41.10  
  Purchase #5 $221.35   10.225%   $243.983   $243.98   $244.00   $244.00  
  Purchase #6 $8.76   8.157%   $9.4746   $9.47   $9.45   $9.50  
  Purchase #7 $171.37   13.448%   $194.4158   $194.42   $194.40   $194.40  
  7 purchase totals = $1,038.77       $1,149.5201   $1,149.52   $1,149.50   $1,149.50