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 $94.43   11.153%   $104.9618   $104.96   $104.95   $105.00  
  Purchase #2 $90.83   5.210%   $95.5622   $95.56   $95.55   $95.60  
  Purchase #3 $109.79   4.129%   $114.3232   $114.32   $114.30   $114.30  
  Purchase #4 $177.45   13.673%   $201.7127   $201.71   $201.70   $201.70  
  Purchase #5 $14.72   4.280%   $15.35   $15.35   $15.35   $15.40  
  Purchase #6 $165.72   3.842%   $172.087   $172.09   $172.10   $172.10  
  Purchase #7 $239.66   11.742%   $267.8009   $267.80   $267.80   $267.80  
  7 purchase totals = $892.60       $971.7978   $971.79   $971.75   $971.90