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 $227.92   10.228%   $251.2317   $251.23   $251.25   $251.20  
  Purchase #2 $43.38   8.228%   $46.9493   $46.95   $46.95   $46.90  
  Purchase #3 $120.58   5.838%   $127.6195   $127.62   $127.60   $127.60  
  Purchase #4 $166.98   6.143%   $177.2376   $177.24   $177.25   $177.20  
  Purchase #5 $26.75   6.760%   $28.5583   $28.56   $28.55   $28.60  
  Purchase #6 $244.75   11.843%   $273.7357   $273.74   $273.75   $273.70  
  Purchase #7 $122.27   9.171%   $133.4834   $133.48   $133.50   $133.50  
  7 purchase totals = $952.63       $1,038.8155   $1,038.82   $1,038.85   $1,038.70