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 $43.93   9.161%   $47.9544   $47.95   $47.95   $48.00  
  Purchase #2 $229.53   5.245%   $241.5688   $241.57   $241.55   $241.60  
  Purchase #3 $128.56   8.676%   $139.7139   $139.71   $139.70   $139.70  
  Purchase #4 $91.99   8.247%   $99.5764   $99.58   $99.60   $99.60  
  Purchase #5 $196.82   6.858%   $210.3179   $210.32   $210.30   $210.30  
  Purchase #6 $45.92   13.531%   $52.1334   $52.13   $52.15   $52.10  
  Purchase #7 $34.36   6.862%   $36.7178   $36.72   $36.70   $36.70  
  7 purchase totals = $771.11       $827.9826   $827.98   $827.95   $828.00