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 $183.57   5.823%   $194.2593   $194.26   $194.25   $194.30  
  Purchase #2 $22.46   6.688%   $23.9621   $23.96   $23.95   $24.00  
  Purchase #3 $38.90   12.277%   $43.6758   $43.68   $43.70   $43.70  
  Purchase #4 $214.87   4.754%   $225.0849   $225.08   $225.10   $225.10  
  Purchase #5 $92.54   13.455%   $104.9913   $104.99   $105.00   $105.00  
  Purchase #6 $171.29   12.316%   $192.3861   $192.39   $192.40   $192.40  
  Purchase #7 $137.48   3.873%   $142.8046   $142.80   $142.80   $142.80  
  7 purchase totals = $861.11       $927.1641   $927.16   $927.20   $927.30