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 $186.58   5.480%   $196.8046   $196.80   $196.80   $196.80  
  Purchase #2 $168.76   8.837%   $183.6733   $183.67   $183.65   $183.70  
  Purchase #3 $96.29   10.781%   $106.671   $106.67   $106.65   $106.70  
  Purchase #4 $111.30   4.313%   $116.1004   $116.10   $116.10   $116.10  
  Purchase #5 $123.32   6.205%   $130.972   $130.97   $130.95   $131.00  
  Purchase #6 $26.90   11.838%   $30.0844   $30.08   $30.10   $30.10  
  Purchase #7 $166.69   4.718%   $174.5544   $174.55   $174.55   $174.60  
  7 purchase totals = $879.84       $938.8601   $938.84   $938.80   $939.00