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 $59.45   3.720%   $61.6615   $61.66   $61.65   $61.70  
  Purchase #2 $104.88   5.231%   $110.3663   $110.37   $110.35   $110.40  
  Purchase #3 $73.50   8.855%   $80.0084   $80.01   $80.00   $80.00  
  Purchase #4 $198.71   7.223%   $213.0628   $213.06   $213.05   $213.10  
  Purchase #5 $193.48   3.509%   $200.2692   $200.27   $200.25   $200.30  
  Purchase #6 $165.56   7.287%   $177.6244   $177.62   $177.60   $177.60  
  Purchase #7 $160.56   6.291%   $170.6608   $170.66   $170.65   $170.70  
  7 purchase totals = $956.14       $1,013.6534   $1,013.65   $1,013.55   $1,013.80