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 $52.52   6.589%   $55.9805   $55.98   $56.00   $56.00  
  Purchase #2 $221.42   11.694%   $247.3129   $247.31   $247.30   $247.30  
  Purchase #3 $147.77   4.461%   $154.362   $154.36   $154.35   $154.40  
  Purchase #4 $107.36   12.786%   $121.087   $121.09   $121.10   $121.10  
  Purchase #5 $168.95   5.141%   $177.6357   $177.64   $177.65   $177.60  
  Purchase #6 $87.55   3.379%   $90.5083   $90.51   $90.50   $90.50  
  Purchase #7 $106.92   7.203%   $114.6214   $114.62   $114.60   $114.60  
  7 purchase totals = $892.49       $961.5078   $961.51   $961.50   $961.50