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 $98.41   12.363%   $110.5764   $110.58   $110.60   $110.60  
  Purchase #2 $201.91   7.377%   $216.8049   $216.80   $216.80   $216.80  
  Purchase #3 $50.60   12.551%   $56.9508   $56.95   $56.95   $57.00  
  Purchase #4 $34.53   4.602%   $36.1191   $36.12   $36.10   $36.10  
  Purchase #5 $236.55   9.724%   $259.5521   $259.55   $259.55   $259.60  
  Purchase #6 $118.98   4.841%   $124.7398   $124.74   $124.75   $124.70  
  Purchase #7 $44.38   11.188%   $49.3452   $49.35   $49.35   $49.30  
  7 purchase totals = $785.36       $854.0883   $854.09   $854.10   $854.10