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 $76.25   11.230%   $84.8129   $84.81   $84.80   $84.80  
  Purchase #2 $152.96   8.561%   $166.0549   $166.05   $166.05   $166.10  
  Purchase #3 $235.75   11.324%   $262.4463   $262.45   $262.45   $262.40  
  Purchase #4 $32.93   4.836%   $34.5225   $34.52   $34.50   $34.50  
  Purchase #5 $23.44   6.129%   $24.8766   $24.88   $24.90   $24.90  
  Purchase #6 $131.33   4.281%   $136.9522   $136.95   $136.95   $137.00  
  Purchase #7 $249.35   9.813%   $273.8187   $273.82   $273.80   $273.80  
  7 purchase totals = $902.01       $983.4841   $983.48   $983.45   $983.50