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 $184.91   12.292%   $207.6391   $207.64   $207.65   $207.60  
  Purchase #2 $220.50   9.441%   $241.3174   $241.32   $241.30   $241.30  
  Purchase #3 $230.58   5.592%   $243.474   $243.47   $243.45   $243.50  
  Purchase #4 $18.38   3.652%   $19.0512   $19.05   $19.05   $19.10  
  Purchase #5 $104.45   11.294%   $116.2466   $116.25   $116.25   $116.20  
  Purchase #6 $36.29   5.388%   $38.2453   $38.25   $38.25   $38.20  
  Purchase #7 $81.90   5.432%   $86.3488   $86.35   $86.35   $86.30  
  7 purchase totals = $877.01       $952.3224   $952.33   $952.30   $952.20