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 $218.38   11.746%   $244.0309   $244.03   $244.05   $244.00  
  Purchase #2 $96.59   13.873%   $109.9899   $109.99   $110.00   $110.00  
  Purchase #3 $53.80   11.415%   $59.9413   $59.94   $59.95   $59.90  
  Purchase #4 $126.26   11.329%   $140.564   $140.56   $140.55   $140.60  
  Purchase #5 $38.79   5.849%   $41.0588   $41.06   $41.05   $41.10  
  Purchase #6 $220.61   4.477%   $230.4867   $230.49   $230.50   $230.50  
  Purchase #7 $206.37   5.225%   $217.1528   $217.15   $217.15   $217.20  
  7 purchase totals = $960.80       $1,043.2244   $1,043.22   $1,043.25   $1,043.30