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 $193.61   4.178%   $201.699   $201.70   $201.70   $201.70  
  Purchase #2 $38.97   5.815%   $41.2361   $41.24   $41.25   $41.20  
  Purchase #3 $97.52   5.425%   $102.8105   $102.81   $102.80   $102.80  
  Purchase #4 $113.53   3.599%   $117.6159   $117.62   $117.60   $117.60  
  Purchase #5 $167.85   6.339%   $178.49   $178.49   $178.50   $178.50  
  Purchase #6 $174.28   11.803%   $194.8503   $194.85   $194.85   $194.90  
  Purchase #7 $5.71   11.183%   $6.3485   $6.35   $6.35   $6.30  
  7 purchase totals = $791.47       $843.0503   $843.06   $843.05   $843.00