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 $93.48   5.233%   $98.3718   $98.37   $98.35   $98.40  
  Purchase #2 $180.93   3.113%   $186.5624   $186.56   $186.55   $186.60  
  Purchase #3 $155.55   11.731%   $173.7976   $173.80   $173.80   $173.80  
  Purchase #4 $245.44   5.102%   $257.9623   $257.96   $257.95   $258.00  
  Purchase #5 $31.81   12.582%   $35.8123   $35.81   $35.80   $35.80  
  Purchase #6 $244.45   3.295%   $252.5046   $252.50   $252.50   $252.50  
  Purchase #7 $213.58   8.164%   $231.0167   $231.02   $231.00   $231.00  
  7 purchase totals = $1,165.24       $1,236.0277   $1,236.02   $1,235.95   $1,236.10