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 $84.44   8.179%   $91.3463   $91.35   $91.35   $91.30  
  Purchase #2 $127.26   9.757%   $139.6768   $139.68   $139.70   $139.70  
  Purchase #3 $47.78   8.284%   $51.7381   $51.74   $51.75   $51.70  
  Purchase #4 $241.62   12.593%   $272.0472   $272.05   $272.05   $272.00  
  Purchase #5 $198.97   6.518%   $211.9389   $211.94   $211.95   $211.90  
  Purchase #6 $93.66   9.172%   $102.2505   $102.25   $102.25   $102.30  
  Purchase #7 $191.42   4.799%   $200.6062   $200.61   $200.60   $200.60  
  7 purchase totals = $985.15       $1,069.6040   $1,069.62   $1,069.65   $1,069.50