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 $52.61   10.383%   $58.0725   $58.07   $58.05   $58.10  
  Purchase #2 $248.46   4.113%   $258.6792   $258.68   $258.70   $258.70  
  Purchase #3 $115.39   8.854%   $125.6066   $125.61   $125.60   $125.60  
  Purchase #4 $227.59   6.810%   $243.0889   $243.09   $243.10   $243.10  
  Purchase #5 $205.40   11.469%   $228.9573   $228.96   $228.95   $229.00  
  Purchase #6 $143.31   3.715%   $148.634   $148.63   $148.65   $148.60  
  Purchase #7 $60.29   12.207%   $67.6496   $67.65   $67.65   $67.60  
  7 purchase totals = $1,053.05       $1,130.6881   $1,130.69   $1,130.70   $1,130.70