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 $243.84   3.256%   $251.7794   $251.78   $251.80   $251.80  
  Purchase #2 $18.30   5.674%   $19.3383   $19.34   $19.35   $19.30  
  Purchase #3 $229.29   5.233%   $241.2887   $241.29   $241.30   $241.30  
  Purchase #4 $137.78   7.328%   $147.8765   $147.88   $147.90   $147.90  
  Purchase #5 $35.76   6.501%   $38.0848   $38.08   $38.10   $38.10  
  Purchase #6 $182.74   6.108%   $193.9018   $193.90   $193.90   $193.90  
  Purchase #7 $109.41   11.858%   $122.3838   $122.38   $122.40   $122.40  
  7 purchase totals = $957.12       $1,014.6533   $1,014.65   $1,014.75   $1,014.70