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 $207.39   13.471%   $235.3275   $235.33   $235.35   $235.30  
  Purchase #2 $201.81   13.303%   $228.6568   $228.66   $228.65   $228.70  
  Purchase #3 $21.66   13.596%   $24.6049   $24.60   $24.60   $24.60  
  Purchase #4 $175.60   13.406%   $199.1409   $199.14   $199.15   $199.10  
  Purchase #5 $148.43   11.536%   $165.5529   $165.55   $165.55   $165.60  
  Purchase #6 $132.75   8.646%   $144.2276   $144.23   $144.25   $144.20  
  Purchase #7 $83.58   8.251%   $90.4762   $90.48   $90.50   $90.50  
  7 purchase totals = $971.22       $1,087.9868   $1,087.99   $1,088.05   $1,088.00