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 $41.93   5.818%   $44.3695   $44.37   $44.35   $44.40  
  Purchase #2 $56.61   4.212%   $58.9944   $58.99   $59.00   $59.00  
  Purchase #3 $21.47   11.757%   $23.9942   $23.99   $24.00   $24.00  
  Purchase #4 $243.45   4.727%   $254.9579   $254.96   $254.95   $255.00  
  Purchase #5 $127.59   9.612%   $139.854   $139.85   $139.85   $139.90  
  Purchase #6 $192.50   6.768%   $205.5284   $205.53   $205.55   $205.50  
  Purchase #7 $96.31   6.699%   $102.7618   $102.76   $102.75   $102.80  
  7 purchase totals = $779.86       $830.4602   $830.45   $830.45   $830.60