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 $121.57   13.261%   $137.6914   $137.69   $137.70   $137.70  
  Purchase #2 $243.88   8.108%   $263.6538   $263.65   $263.65   $263.70  
  Purchase #3 $52.27   12.396%   $58.7494   $58.75   $58.75   $58.70  
  Purchase #4 $222.45   4.419%   $232.2801   $232.28   $232.30   $232.30  
  Purchase #5 $185.94   4.137%   $193.6323   $193.63   $193.65   $193.60  
  Purchase #6 $196.92   8.840%   $214.3277   $214.33   $214.35   $214.30  
  Purchase #7 $158.63   11.211%   $176.414   $176.41   $176.40   $176.40  
  7 purchase totals = $1,181.66       $1,276.7487   $1,276.74   $1,276.80   $1,276.70