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 $113.95   10.565%   $125.9888   $125.99   $126.00   $126.00  
  Purchase #2 $42.31   8.224%   $45.7896   $45.79   $45.80   $45.80  
  Purchase #3 $219.89   11.441%   $245.0476   $245.05   $245.05   $245.00  
  Purchase #4 $65.74   6.532%   $70.0341   $70.03   $70.05   $70.00  
  Purchase #5 $231.55   6.780%   $247.2491   $247.25   $247.25   $247.20  
  Purchase #6 $212.40   8.140%   $229.6894   $229.69   $229.70   $229.70  
  Purchase #7 $61.57   5.671%   $65.0616   $65.06   $65.05   $65.10  
  7 purchase totals = $947.41       $1,028.8602   $1,028.86   $1,028.90   $1,028.80