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 $16.95   13.458%   $19.2311   $19.23   $19.25   $19.20  
  Purchase #2 $235.33   4.301%   $245.4515   $245.45   $245.45   $245.50  
  Purchase #3 $177.47   11.738%   $198.3014   $198.30   $198.30   $198.30  
  Purchase #4 $122.64   3.148%   $126.5007   $126.50   $126.50   $126.50  
  Purchase #5 $22.69   8.137%   $24.5363   $24.54   $24.55   $24.50  
  Purchase #6 $212.46   11.141%   $236.1302   $236.13   $236.15   $236.10  
  Purchase #7 $208.47   10.704%   $230.7846   $230.78   $230.80   $230.80  
  7 purchase totals = $996.01       $1,080.9358   $1,080.93   $1,081.00   $1,080.90