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 $76.60   12.171%   $85.923   $85.92   $85.90   $85.90  
  Purchase #2 $7.78   9.568%   $8.5244   $8.52   $8.50   $8.50  
  Purchase #3 $32.76   5.521%   $34.5687   $34.57   $34.55   $34.60  
  Purchase #4 $192.36   7.257%   $206.3196   $206.32   $206.30   $206.30  
  Purchase #5 $177.48   9.742%   $194.7701   $194.77   $194.75   $194.80  
  Purchase #6 $158.71   8.280%   $171.8512   $171.85   $171.85   $171.90  
  Purchase #7 $114.89   6.626%   $122.5026   $122.50   $122.50   $122.50  
  7 purchase totals = $760.58       $824.4596   $824.45   $824.35   $824.50