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 $10.80   3.149%   $11.1401   $11.14   $11.15   $11.10  
  Purchase #2 $238.99   13.304%   $270.7852   $270.79   $270.80   $270.80  
  Purchase #3 $122.86   9.307%   $134.2946   $134.29   $134.30   $134.30  
  Purchase #4 $33.95   12.549%   $38.2104   $38.21   $38.20   $38.20  
  Purchase #5 $195.81   3.559%   $202.7789   $202.78   $202.80   $202.80  
  Purchase #6 $246.65   11.478%   $274.9605   $274.96   $274.95   $275.00  
  Purchase #7 $111.91   13.775%   $127.3256   $127.33   $127.35   $127.30  
  7 purchase totals = $960.97       $1,059.4953   $1,059.50   $1,059.55   $1,059.50