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 $228.91   13.861%   $260.6392   $260.64   $260.65   $260.60  
  Purchase #2 $83.36   12.359%   $93.6625   $93.66   $93.65   $93.70  
  Purchase #3 $96.38   4.263%   $100.4887   $100.49   $100.50   $100.50  
  Purchase #4 $56.29   6.865%   $60.1543   $60.15   $60.15   $60.20  
  Purchase #5 $161.78   10.106%   $178.1295   $178.13   $178.15   $178.10  
  Purchase #6 $24.81   11.126%   $27.5704   $27.57   $27.55   $27.60  
  Purchase #7 $70.65   13.789%   $80.3919   $80.39   $80.40   $80.40  
  7 purchase totals = $722.18       $801.0365   $801.03   $801.05   $801.10