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 $61.90   12.451%   $69.6072   $69.61   $69.60   $69.60  
  Purchase #2 $248.40   12.314%   $278.988   $278.99   $279.00   $279.00  
  Purchase #3 $211.71   9.747%   $232.3454   $232.35   $232.35   $232.30  
  Purchase #4 $203.90   9.642%   $223.56   $223.56   $223.55   $223.60  
  Purchase #5 $169.59   12.722%   $191.1652   $191.17   $191.15   $191.20  
  Purchase #6 $116.50   12.167%   $130.6746   $130.67   $130.65   $130.70  
  Purchase #7 $59.25   11.866%   $66.2806   $66.28   $66.30   $66.30  
  7 purchase totals = $1,071.25       $1,192.6210   $1,192.63   $1,192.60   $1,192.70