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 $239.91   13.647%   $272.6505   $272.65   $272.65   $272.70  
  Purchase #2 $153.50   9.349%   $167.8507   $167.85   $167.85   $167.90  
  Purchase #3 $51.31   13.802%   $58.3918   $58.39   $58.40   $58.40  
  Purchase #4 $188.47   6.624%   $200.9543   $200.95   $200.95   $201.00  
  Purchase #5 $41.37   7.688%   $44.5505   $44.55   $44.55   $44.60  
  Purchase #6 $10.42   11.471%   $11.6153   $11.62   $11.60   $11.60  
  Purchase #7 $232.79   3.647%   $241.2799   $241.28   $241.30   $241.30  
  7 purchase totals = $917.77       $997.2930   $997.29   $997.30   $997.50