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 $33.45   10.693%   $37.0268   $37.03   $37.05   $37.00  
  Purchase #2 $88.95   6.745%   $94.9497   $94.95   $94.95   $94.90  
  Purchase #3 $226.79   6.552%   $241.6493   $241.65   $241.65   $241.60  
  Purchase #4 $123.53   11.176%   $137.3357   $137.34   $137.35   $137.30  
  Purchase #5 $12.87   13.272%   $14.5781   $14.58   $14.60   $14.60  
  Purchase #6 $157.25   4.234%   $163.908   $163.91   $163.90   $163.90  
  Purchase #7 $211.85   3.723%   $219.7372   $219.74   $219.75   $219.70  
  7 purchase totals = $854.69       $909.1848   $909.20   $909.25   $909.00