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 $61.54   13.737%   $69.9937   $69.99   $70.00   $70.00  
  Purchase #2 $27.26   5.349%   $28.7181   $28.72   $28.70   $28.70  
  Purchase #3 $131.79   5.475%   $139.0055   $139.01   $139.00   $139.00  
  Purchase #4 $163.94   10.178%   $180.6258   $180.63   $180.65   $180.60  
  Purchase #5 $194.62   13.197%   $220.304   $220.30   $220.30   $220.30  
  Purchase #6 $227.33   10.300%   $250.745   $250.75   $250.75   $250.70  
  Purchase #7 $239.77   9.582%   $262.7448   $262.74   $262.75   $262.70  
  7 purchase totals = $1,046.25       $1,152.1369   $1,152.14   $1,152.15   $1,152.00