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 $65.76   11.159%   $73.0982   $73.10   $73.10   $73.10  
  Purchase #2 $185.74   9.810%   $203.9611   $203.96   $203.95   $204.00  
  Purchase #3 $64.71   4.693%   $67.7468   $67.75   $67.75   $67.70  
  Purchase #4 $178.76   7.591%   $192.3297   $192.33   $192.35   $192.30  
  Purchase #5 $108.96   8.724%   $118.4657   $118.47   $118.45   $118.50  
  Purchase #6 $47.93   11.737%   $53.5555   $53.56   $53.55   $53.60  
  Purchase #7 $181.55   8.847%   $197.6117   $197.61   $197.60   $197.60  
  7 purchase totals = $833.41       $906.7687   $906.78   $906.75   $906.80