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 $84.56   10.652%   $93.5673   $93.57   $93.55   $93.60  
  Purchase #2 $59.99   8.489%   $65.0826   $65.08   $65.10   $65.10  
  Purchase #3 $61.81   8.231%   $66.8976   $66.90   $66.90   $66.90  
  Purchase #4 $227.94   5.820%   $241.2061   $241.21   $241.20   $241.20  
  Purchase #5 $175.60   3.385%   $181.5441   $181.54   $181.55   $181.50  
  Purchase #6 $239.51   6.243%   $254.4626   $254.46   $254.45   $254.50  
  Purchase #7 $78.61   4.468%   $82.1223   $82.12   $82.10   $82.10  
  7 purchase totals = $928.02       $984.8826   $984.88   $984.85   $984.90