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 $243.76   8.615%   $264.7599   $264.76   $264.75   $264.80  
  Purchase #2 $85.87   3.306%   $88.7089   $88.71   $88.70   $88.70  
  Purchase #3 $154.92   8.209%   $167.6374   $167.64   $167.65   $167.60  
  Purchase #4 $58.64   8.335%   $63.5276   $63.53   $63.55   $63.50  
  Purchase #5 $210.25   5.716%   $222.2679   $222.27   $222.25   $222.30  
  Purchase #6 $160.74   10.752%   $178.0228   $178.02   $178.00   $178.00  
  Purchase #7 $36.69   4.149%   $38.2123   $38.21   $38.20   $38.20  
  7 purchase totals = $950.87       $1,023.1368   $1,023.14   $1,023.10   $1,023.10