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 $44.81   11.393%   $49.9152   $49.92   $49.90   $49.90  
  Purchase #2 $93.56   9.760%   $102.6915   $102.69   $102.70   $102.70  
  Purchase #3 $250.25   9.803%   $274.782   $274.78   $274.80   $274.80  
  Purchase #4 $185.37   10.749%   $205.2954   $205.30   $205.30   $205.30  
  Purchase #5 $126.88   8.229%   $137.321   $137.32   $137.30   $137.30  
  Purchase #6 $165.60   11.125%   $184.023   $184.02   $184.00   $184.00  
  Purchase #7 $106.82   8.110%   $115.4831   $115.48   $115.50   $115.50  
  7 purchase totals = $973.29       $1,069.5112   $1,069.51   $1,069.50   $1,069.50