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 $23.31   8.344%   $25.255   $25.26   $25.25   $25.30  
  Purchase #2 $142.76   3.358%   $147.5539   $147.55   $147.55   $147.60  
  Purchase #3 $94.97   9.450%   $103.9447   $103.94   $103.95   $103.90  
  Purchase #4 $158.29   11.182%   $175.99   $175.99   $176.00   $176.00  
  Purchase #5 $203.66   12.560%   $229.2397   $229.24   $229.25   $229.20  
  Purchase #6 $242.45   13.689%   $275.639   $275.64   $275.65   $275.60  
  Purchase #7 $70.51   3.716%   $73.1302   $73.13   $73.15   $73.10  
  7 purchase totals = $935.95       $1,030.7525   $1,030.75   $1,030.80   $1,030.70