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 $105.52   6.151%   $112.0105   $112.01   $112.00   $112.00  
  Purchase #2 $244.37   10.413%   $269.8162   $269.82   $269.80   $269.80  
  Purchase #3 $48.60   13.782%   $55.2981   $55.30   $55.30   $55.30  
  Purchase #4 $228.91   5.565%   $241.6488   $241.65   $241.65   $241.60  
  Purchase #5 $176.41   10.491%   $194.9172   $194.92   $194.90   $194.90  
  Purchase #6 $243.52   13.477%   $276.3392   $276.34   $276.35   $276.30  
  Purchase #7 $49.73   13.678%   $56.5321   $56.53   $56.55   $56.50  
  7 purchase totals = $1,097.06       $1,206.5621   $1,206.57   $1,206.55   $1,206.40