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 $171.53   6.126%   $182.0379   $182.04   $182.05   $182.00  
  Purchase #2 $157.99   7.824%   $170.3511   $170.35   $170.35   $170.40  
  Purchase #3 $22.45   4.474%   $23.4544   $23.45   $23.45   $23.50  
  Purchase #4 $246.88   11.806%   $276.0267   $276.03   $276.05   $276.00  
  Purchase #5 $186.84   3.366%   $193.129   $193.13   $193.15   $193.10  
  Purchase #6 $166.96   3.352%   $172.5565   $172.56   $172.55   $172.60  
  Purchase #7 $33.90   5.330%   $35.7069   $35.71   $35.70   $35.70  
  7 purchase totals = $986.55       $1,053.2625   $1,053.27   $1,053.30   $1,053.30