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 $8.79   3.668%   $9.1124   $9.11   $9.10   $9.10  
  Purchase #2 $81.33   12.160%   $91.2197   $91.22   $91.20   $91.20  
  Purchase #3 $119.71   8.180%   $129.5023   $129.50   $129.50   $129.50  
  Purchase #4 $145.55   8.537%   $157.9756   $157.98   $158.00   $158.00  
  Purchase #5 $186.57   3.262%   $192.6559   $192.66   $192.65   $192.70  
  Purchase #6 $212.28   11.852%   $237.4394   $237.44   $237.45   $237.40  
  Purchase #7 $121.68   6.224%   $129.2534   $129.25   $129.25   $129.30  
  7 purchase totals = $875.91       $947.1587   $947.16   $947.15   $947.20