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 $170.44   13.836%   $194.0221   $194.02   $194.00   $194.00  
  Purchase #2 $45.76   4.216%   $47.6892   $47.69   $47.70   $47.70  
  Purchase #3 $245.81   4.637%   $257.2082   $257.21   $257.20   $257.20  
  Purchase #4 $91.27   4.728%   $95.5852   $95.59   $95.60   $95.60  
  Purchase #5 $243.48   9.738%   $267.1901   $267.19   $267.20   $267.20  
  Purchase #6 $56.45   8.515%   $61.2567   $61.26   $61.25   $61.30  
  Purchase #7 $21.96   11.575%   $24.5019   $24.50   $24.50   $24.50  
  7 purchase totals = $875.17       $947.4534   $947.46   $947.45   $947.50