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 $93.79   3.750%   $97.3071   $97.31   $97.30   $97.30  
  Purchase #2 $53.77   4.453%   $56.1644   $56.16   $56.15   $56.20  
  Purchase #3 $135.80   4.267%   $141.5946   $141.59   $141.60   $141.60  
  Purchase #4 $188.66   3.683%   $195.6083   $195.61   $195.60   $195.60  
  Purchase #5 $41.95   9.240%   $45.8262   $45.83   $45.85   $45.80  
  Purchase #6 $38.53   6.797%   $41.1489   $41.15   $41.15   $41.10  
  Purchase #7 $12.30   3.119%   $12.6836   $12.68   $12.70   $12.70  
  7 purchase totals = $564.80       $590.3331   $590.33   $590.35   $590.30