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 $121.32   8.487%   $131.6164   $131.62   $131.60   $131.60  
  Purchase #2 $99.95   3.719%   $103.6671   $103.67   $103.65   $103.70  
  Purchase #3 $171.56   11.443%   $191.1916   $191.19   $191.20   $191.20  
  Purchase #4 $125.82   3.210%   $129.8588   $129.86   $129.85   $129.90  
  Purchase #5 $184.92   11.345%   $205.8992   $205.90   $205.90   $205.90  
  Purchase #6 $134.68   3.855%   $139.8719   $139.87   $139.85   $139.90  
  Purchase #7 $45.83   4.298%   $47.7998   $47.80   $47.80   $47.80  
  7 purchase totals = $884.08       $949.9048   $949.91   $949.85   $950.00