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 $242.62   11.201%   $269.7959   $269.80   $269.80   $269.80  
  Purchase #2 $151.81   8.173%   $164.2174   $164.22   $164.20   $164.20  
  Purchase #3 $141.79   11.668%   $158.3341   $158.33   $158.35   $158.30  
  Purchase #4 $31.53   12.168%   $35.3666   $35.37   $35.35   $35.40  
  Purchase #5 $9.64   11.205%   $10.7202   $10.72   $10.70   $10.70  
  Purchase #6 $117.73   4.823%   $123.4081   $123.41   $123.40   $123.40  
  Purchase #7 $211.59   10.573%   $233.9614   $233.96   $233.95   $234.00  
  7 purchase totals = $906.71       $995.8037   $995.81   $995.75   $995.80