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 $247.79   6.446%   $263.7625   $263.76   $263.75   $263.80  
  Purchase #2 $113.42   5.301%   $119.4324   $119.43   $119.45   $119.40  
  Purchase #3 $38.64   9.704%   $42.3896   $42.39   $42.40   $42.40  
  Purchase #4 $74.26   4.835%   $77.8505   $77.85   $77.85   $77.90  
  Purchase #5 $70.44   6.356%   $74.9172   $74.92   $74.90   $74.90  
  Purchase #6 $58.88   3.485%   $60.932   $60.93   $60.95   $60.90  
  Purchase #7 $201.58   5.580%   $212.8282   $212.83   $212.85   $212.80  
  7 purchase totals = $805.01       $852.1124   $852.11   $852.15   $852.10