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 $61.50   11.318%   $68.4606   $68.46   $68.45   $68.50  
  Purchase #2 $117.36   7.173%   $125.7782   $125.78   $125.80   $125.80  
  Purchase #3 $203.50   13.260%   $230.4841   $230.48   $230.50   $230.50  
  Purchase #4 $121.67   6.337%   $129.3802   $129.38   $129.40   $129.40  
  Purchase #5 $141.63   13.629%   $160.9328   $160.93   $160.95   $160.90  
  Purchase #6 $14.56   12.543%   $16.3863   $16.39   $16.40   $16.40  
  Purchase #7 $222.92   6.603%   $237.6394   $237.64   $237.65   $237.60  
  7 purchase totals = $883.14       $969.0616   $969.06   $969.15   $969.10