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 $82.51   12.504%   $92.8271   $92.83   $92.85   $92.80  
  Purchase #2 $63.81   9.874%   $70.1106   $70.11   $70.10   $70.10  
  Purchase #3 $158.47   6.688%   $169.0685   $169.07   $169.05   $169.10  
  Purchase #4 $98.97   9.264%   $108.1386   $108.14   $108.15   $108.10  
  Purchase #5 $170.57   6.463%   $181.5939   $181.59   $181.60   $181.60  
  Purchase #6 $90.44   9.706%   $99.2181   $99.22   $99.20   $99.20  
  Purchase #7 $229.85   4.443%   $240.0622   $240.06   $240.05   $240.10  
  7 purchase totals = $894.62       $961.0190   $961.02   $961.00   $961.00