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 $61.56   10.773%   $68.1919   $68.19   $68.20   $68.20  
  Purchase #2 $100.51   6.703%   $107.2472   $107.25   $107.25   $107.20  
  Purchase #3 $11.60   9.224%   $12.67   $12.67   $12.65   $12.70  
  Purchase #4 $112.83   9.683%   $123.7553   $123.76   $123.75   $123.80  
  Purchase #5 $223.51   8.704%   $242.9643   $242.96   $242.95   $243.00  
  Purchase #6 $107.36   11.264%   $119.453   $119.45   $119.45   $119.50  
  Purchase #7 $38.52   12.443%   $43.313   $43.31   $43.30   $43.30  
  7 purchase totals = $655.89       $717.5947   $717.59   $717.55   $717.70