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 $220.84   9.466%   $241.7447   $241.74   $241.75   $241.70  
  Purchase #2 $87.81   6.640%   $93.6406   $93.64   $93.65   $93.60  
  Purchase #3 $34.64   9.832%   $38.0458   $38.05   $38.05   $38.00  
  Purchase #4 $164.33   9.694%   $180.2602   $180.26   $180.25   $180.30  
  Purchase #5 $67.66   9.626%   $74.173   $74.17   $74.15   $74.20  
  Purchase #6 $250.98   5.424%   $264.5932   $264.59   $264.60   $264.60  
  Purchase #7 $97.27   5.380%   $102.5031   $102.50   $102.50   $102.50  
  7 purchase totals = $923.53       $994.9606   $994.95   $994.95   $994.90