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 $153.86   8.736%   $167.3012   $167.30   $167.30   $167.30  
  Purchase #2 $205.86   6.153%   $218.5266   $218.53   $218.55   $218.50  
  Purchase #3 $52.52   10.424%   $57.9947   $57.99   $58.00   $58.00  
  Purchase #4 $45.66   11.859%   $51.0748   $51.07   $51.05   $51.10  
  Purchase #5 $88.64   5.649%   $93.6473   $93.65   $93.65   $93.60  
  Purchase #6 $109.81   9.850%   $120.6263   $120.63   $120.65   $120.60  
  Purchase #7 $173.25   10.535%   $191.5019   $191.50   $191.50   $191.50  
  7 purchase totals = $829.60       $900.6728   $900.67   $900.70   $900.60