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 $42.82   4.213%   $44.624   $44.62   $44.60   $44.60  
  Purchase #2 $77.36   5.610%   $81.6999   $81.70   $81.70   $81.70  
  Purchase #3 $145.32   4.211%   $151.4394   $151.44   $151.45   $151.40  
  Purchase #4 $203.67   8.301%   $220.5766   $220.58   $220.60   $220.60  
  Purchase #5 $7.53   13.473%   $8.5445   $8.54   $8.55   $8.50  
  Purchase #6 $94.71   11.836%   $105.9199   $105.92   $105.90   $105.90  
  Purchase #7 $202.42   4.832%   $212.2009   $212.20   $212.20   $212.20  
  7 purchase totals = $773.83       $825.0052   $825.00   $825.00   $824.90