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 $52.95   3.859%   $54.9933   $54.99   $55.00   $55.00  
  Purchase #2 $246.39   8.457%   $267.2272   $267.23   $267.25   $267.20  
  Purchase #3 $219.46   10.843%   $243.256   $243.26   $243.25   $243.30  
  Purchase #4 $134.28   9.679%   $147.277   $147.28   $147.30   $147.30  
  Purchase #5 $82.46   9.526%   $90.3151   $90.32   $90.30   $90.30  
  Purchase #6 $69.81   6.656%   $74.4566   $74.46   $74.45   $74.50  
  Purchase #7 $121.34   3.275%   $125.3139   $125.31   $125.30   $125.30  
  7 purchase totals = $926.69       $1,002.8391   $1,002.85   $1,002.85   $1,002.90