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 $248.62   13.515%   $282.221   $282.22   $282.20   $282.20  
  Purchase #2 $10.83   3.622%   $11.2223   $11.22   $11.20   $11.20  
  Purchase #3 $55.33   3.483%   $57.2571   $57.26   $57.25   $57.30  
  Purchase #4 $108.81   13.309%   $123.2915   $123.29   $123.30   $123.30  
  Purchase #5 $95.97   6.276%   $101.9931   $101.99   $102.00   $102.00  
  Purchase #6 $138.77   7.607%   $149.3262   $149.33   $149.35   $149.30  
  Purchase #7 $115.44   6.132%   $122.5188   $122.52   $122.50   $122.50  
  7 purchase totals = $773.77       $847.8300   $847.83   $847.80   $847.80