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 $206.71   9.414%   $226.1697   $226.17   $226.15   $226.20  
  Purchase #2 $32.47   7.596%   $34.9364   $34.94   $34.95   $34.90  
  Purchase #3 $227.52   6.683%   $242.7252   $242.73   $242.75   $242.70  
  Purchase #4 $73.57   9.801%   $80.7806   $80.78   $80.80   $80.80  
  Purchase #5 $5.27   5.493%   $5.5595   $5.56   $5.55   $5.60  
  Purchase #6 $177.53   4.586%   $185.6715   $185.67   $185.65   $185.70  
  Purchase #7 $173.27   7.432%   $186.1474   $186.15   $186.15   $186.10  
  7 purchase totals = $896.34       $961.9903   $962.00   $962.00   $962.00