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 $188.52   12.667%   $212.3998   $212.40   $212.40   $212.40  
  Purchase #2 $229.46   9.230%   $250.6392   $250.64   $250.65   $250.60  
  Purchase #3 $69.78   8.341%   $75.6003   $75.60   $75.60   $75.60  
  Purchase #4 $66.80   9.231%   $72.9663   $72.97   $72.95   $73.00  
  Purchase #5 $127.40   4.853%   $133.5827   $133.58   $133.60   $133.60  
  Purchase #6 $181.43   10.334%   $200.179   $200.18   $200.20   $200.20  
  Purchase #7 $239.95   5.341%   $252.7657   $252.77   $252.75   $252.80  
  7 purchase totals = $1,103.34       $1,198.1330   $1,198.14   $1,198.15   $1,198.20