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 $82.86   11.716%   $92.5679   $92.57   $92.55   $92.60  
  Purchase #2 $153.63   10.695%   $170.0607   $170.06   $170.05   $170.10  
  Purchase #3 $47.57   12.613%   $53.57   $53.57   $53.55   $53.60  
  Purchase #4 $68.41   8.538%   $74.2508   $74.25   $74.25   $74.30  
  Purchase #5 $204.88   9.154%   $223.6347   $223.63   $223.65   $223.60  
  Purchase #6 $115.55   11.721%   $129.0936   $129.09   $129.10   $129.10  
  Purchase #7 $134.95   5.216%   $141.989   $141.99   $142.00   $142.00  
  7 purchase totals = $807.85       $885.1667   $885.16   $885.15   $885.30