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 $37.69   9.564%   $41.2947   $41.29   $41.30   $41.30  
  Purchase #2 $55.85   10.147%   $61.5171   $61.52   $61.50   $61.50  
  Purchase #3 $148.30   10.458%   $163.8092   $163.81   $163.80   $163.80  
  Purchase #4 $30.61   7.756%   $32.9841   $32.98   $33.00   $33.00  
  Purchase #5 $186.27   13.642%   $211.681   $211.68   $211.70   $211.70  
  Purchase #6 $176.58   4.820%   $185.0912   $185.09   $185.10   $185.10  
  Purchase #7 $208.90   5.297%   $219.9654   $219.97   $219.95   $220.00  
  7 purchase totals = $844.20       $916.3427   $916.34   $916.35   $916.40