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 $191.90   9.348%   $209.8388   $209.84   $209.85   $209.80  
  Purchase #2 $115.70   7.331%   $124.182   $124.18   $124.20   $124.20  
  Purchase #3 $142.39   9.177%   $155.4571   $155.46   $155.45   $155.50  
  Purchase #4 $177.45   9.617%   $194.5154   $194.52   $194.50   $194.50  
  Purchase #5 $115.89   5.321%   $122.0565   $122.06   $122.05   $122.10  
  Purchase #6 $155.76   3.856%   $161.7661   $161.77   $161.75   $161.80  
  Purchase #7 $85.32   3.559%   $88.3565   $88.36   $88.35   $88.40  
  7 purchase totals = $984.41       $1,056.1724   $1,056.19   $1,056.15   $1,056.30