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 $234.95   10.204%   $258.9243   $258.92   $258.90   $258.90  
  Purchase #2 $195.77   3.571%   $202.7609   $202.76   $202.75   $202.80  
  Purchase #3 $246.47   7.564%   $265.113   $265.11   $265.10   $265.10  
  Purchase #4 $99.28   13.245%   $112.4296   $112.43   $112.45   $112.40  
  Purchase #5 $248.59   8.602%   $269.9737   $269.97   $269.95   $270.00  
  Purchase #6 $147.72   7.715%   $159.1166   $159.12   $159.10   $159.10  
  Purchase #7 $201.41   6.523%   $214.548   $214.55   $214.55   $214.50  
  7 purchase totals = $1,374.19       $1,482.8661   $1,482.86   $1,482.80   $1,482.80