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 $150.81   11.693%   $168.4442   $168.44   $168.45   $168.40  
  Purchase #2 $24.43   10.327%   $26.9529   $26.95   $26.95   $27.00  
  Purchase #3 $219.71   11.398%   $244.7525   $244.75   $244.75   $244.80  
  Purchase #4 $53.71   12.481%   $60.4135   $60.41   $60.40   $60.40  
  Purchase #5 $67.32   8.272%   $72.8887   $72.89   $72.90   $72.90  
  Purchase #6 $119.38   12.537%   $134.3467   $134.35   $134.35   $134.30  
  Purchase #7 $238.60   12.823%   $269.1957   $269.20   $269.20   $269.20  
  7 purchase totals = $873.96       $976.9942   $976.99   $977.00   $977.00