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 $219.39   10.195%   $241.7568   $241.76   $241.75   $241.80  
  Purchase #2 $98.45   13.476%   $111.7171   $111.72   $111.70   $111.70  
  Purchase #3 $183.84   10.580%   $203.2903   $203.29   $203.30   $203.30  
  Purchase #4 $36.72   4.809%   $38.4859   $38.49   $38.50   $38.50  
  Purchase #5 $167.94   9.613%   $184.0841   $184.08   $184.10   $184.10  
  Purchase #6 $27.43   12.788%   $30.9377   $30.94   $30.95   $30.90  
  Purchase #7 $167.44   5.131%   $176.0313   $176.03   $176.05   $176.00  
  7 purchase totals = $901.21       $986.3032   $986.31   $986.35   $986.30